Nickel complex hydroxide particles and nonaqueous electrolyte secondary battery

ABSTRACT

Disclosed are: nickel complex hydroxide particles that have small and uniform particle diameters; and a method by which the nickel complex hydroxide particles can be produced. Specifically disclosed is a method for producing a nickel complex hydroxide by a crystallization reaction, which comprises: a nucleation step in which nucleation is carried out, while controlling an aqueous solution for nucleation containing an ammonium ion supplying material and a metal compound that contains nickel to have a pH of 12.0-13.4 at a liquid temperature of 25° C.; and a particle growth step in which nuclei are grown, while controlling an aqueous solution for particle growth containing the nuclei, which have been formed in the nucleation step, to have a pH of 10.5-12.0 at a liquid temperature of 25° C. In this connection, the pH in the particle growth step is controlled to be less than the pH in the nucleation step.

TECHNICAL FIELD

The present invention relates to nickel composite hydroxide particlesand a nonaqueous electrolyte secondary battery. More particularly, thepresent invention relates to nickel composite hydroxide particles and aprocess for producing the same, a cathode active material for anonaqueous electrolyte secondary battery and a process for producing thesame, and a nonaqueous electrolyte secondary battery.

BACKGROUND ART

In recent years, along with the spread of mobile electronic devices suchas mobile phones and notebook-sized personal computers, development of asmall and light nonaqueous electrolyte secondary battery having a highenergy density has been earnestly desired. In addition, development of ahigh power secondary battery has been earnestly desired as a battery forelectric automobiles typified by hybrid automobiles. The secondarybattery which meets the above requirement is a lithium ion secondarybattery. The lithium ion secondary battery is composed of a negativeelectrode, a positive electrode, an electrolyte and the like, and amaterial capable of desorbing and inserting lithium has been used as anactive material for the negative electrode and the positive electrode.

Research and development of the lithium ion secondary batteries havebeen extensively carried out at present. Among them, the practicalapplication of a lithium ion secondary battery in which a layer orspinel type lithium metal composite oxide is used as a positiveelectrode material has been progressed as a battery having a high energydensity, since the battery gives a high voltage as high as 4 V.

As a positive electrode material for use in the lithium ion secondarybattery, there have been hitherto proposed lithium composite oxides suchas lithium cobalt composite oxide (LiCoO₂) which can be relativelyeasily synthesized, lithium-nickel composite oxide (LiNiO₂) in whichnickel being less expensive than cobalt is used, lithium nickel cobaltmanganese composite oxide (LiNi_(1/3)CO_(1/3)Mn_(1/3)O₂), and lithiummanganese composite oxide (LiMn₂O₄) in which manganese is used.

In order to impart favorable performance (high cycle characteristic, lowresistance and high power) to a positive electrode, it has been requiredfor the positive electrode material to be composed of particles having auniform and appropriate particle diameter. This is because the reactionarea of the material with the electrolyte cannot be sufficiently ensuredwhen a material having a large particle diameter and a small specificsurface area is used, and because there arise defects such as loweringof battery capacity and increase of reaction resistance when a materialhaving a broad particle size distribution is used. Incidentally, thereason why the battery capacity is lowered is that the voltage appliedto the particles in the electrode becomes uneven, and thereby finerparticles selectively deteriorate when charge and discharge arerepeated.

Additionally, it is effective for increasing the output of a battery toshorten the transferring distance of lithium ions between a positiveelectrode and a negative electrode. Therefore, it has been desired tothin the positive electrode plate, and therefore, cathode activematerial particles having a smaller particle diameter are useful forthis desire.

Accordingly, it is necessary to produce the above-mentionedlithium-nickel composite oxide particles having a small particlediameter and a uniform particle diameter.

The lithium-nickel composite oxide is usually prepared from a compositehydroxide. Therefore, in order to prepare a lithium-nickel compositeoxide particle having a small particle diameter and a uniform particlediameter, it is necessary to use a composite hydroxide having a smallparticle diameter and a uniform particle diameter as a startingmaterial. In other words, in order to produce a final product, that is,a lithium ion secondary battery having high performance by improvingperformance of a positive electrode material, it is necessary to use acomposite hydroxide composed of particles having a small particlediameter and a narrow particle size distribution as a compositehydroxide which is employed as the source material of the lithium-nickelcomposite oxide for forming the positive electrode material.

Patent Document 1 discloses a lithium composite oxide in the form ofparticles having a particle size distribution in which the averageparticle diameter D50, which means a particle diameter of the particleshaving an accumulation frequency of 50%, is 3 to 15 μm, and in which theminimum particle diameter is not smaller than 0.5 μm, and the maximumparticle diameter is not greater than 50 μm in the particle sizedistribution curve; and in the relationship between D10 which means aparticle diameter of the particles having an accumulation frequency of10% and D90 which means a particle diameter having an accumulationfrequency of 90%, D10/D50 is from 0.60 to 0.90, and D10/D90 is from 0.30to 0.70. In addition, this document discloses that a lithium ionnonaqueous electrolytic solution secondary battery having excellentoutput characteristics and a small lowering of cycle characteristics canbe obtained by using this lithium composite oxide, since the lithiumcomposite oxide has high repletion property, excellent charge anddischarge capacity characteristics and high power characteristics, andis not deteriorated even under the conditions such as a large chargingand discharging load.

In addition, various processes for producing composite hydroxides havebeen proposed (see for example, Patent Documents 2 and 3).

Patent Document 2 proposes a method for producing a cathode activematerial for nonaqueous electrolyte batteries, in which a precursor, anoxide or a hydroxide is obtained by a process comprising charging areaction vessel with an aqueous solution containing at least two kindsof transition metal salts or at least two kinds of aqueous solutionseach of which contains a different transition metal with each other, andan alkali solution at the same time, and carrying out coprecipitationunder the existence of a reducing agent or while blowing an inert gasinto the solution.

Patent Document 3 also discloses a method for producing a cathode activematerial for a lithium secondary battery. This document discloses thatlithium-coprecipitated composite metal salt particles having anapproximately spherical shape are prepared with a reaction vessel bycontinuously feeding an aqueous solution of a composite metal salt inwhich the concentration of the salt is controlled by dissolving a salthaving an element which constitutes the above-mentioned active substancein water, a water-soluble complexing agent which forms a complex saltwith a metal ion, and an aqueous solution of lithium hydroxide to areaction vessel, respectively, to generate a composite metal complexsalt; thereafter decomposing this complex salt with lithium hydroxide,to extract a lithium-coprecipitated composite metal salt; carrying outthe generation and decomposition of the above-mentioned complex saltrepeatedly while circulating in the reaction vessel; overflowing thelithium-coprecipitated composite metal salt to take out. This documentalso discloses that the cathode active material in which the compositemetal salt obtained in this process is used as a source material has ahigh packing density, homogenous components and a nearly sphericalshape.

However, the lithium composite oxide disclosed in Patent Document 1includes very fine particles and coarse particles, since the minimumparticle diameter is 0.5 μm or more, and the maximum particle diameteris not greater than 50 μm in contrast to the average particle diameterof 3 to 15 μm. Therefore, it cannot be said that the range of theparticle size distribution as defined by the above-mentioned D10/D50 andD10/D90 is narrow in the particle diameter distribution. In other words,since it cannot be said that the lithium composite oxide of PatentDocument 1 have particles having uniform particle diameters, it cannotbe expected to improve the performance of the positive electrodematerial even though the lithium composite oxide is employed, and it isdifficult to obtain a lithium ion nonaqueous electrolytic solutionsecondary battery having sufficient performance.

On the other hand, Patent Document 2 discloses a method for producing acomposite oxide. However, since crystals generated are collected byclassification, it is necessary to strictly control the condition forproducing. Therefore, it is difficult to produce in an industrial scale.Moreover, according to this process, even though particles having alarge particle diameter can be obtained, it is difficult to obtainparticles having a small particle diameter.

Patent Document 3 also discloses a continuous crystallization methodwhich comprises taking out a product by overflowing. According to themethod, since the particle size distribution becomes a normaldistribution, and is likely to be spread, it is difficult to obtainalmost uniform particles having a small particle diameter.

As described above, a composite hydroxide which sufficiently improvesthe performance of a lithium-secondary battery has not yet beendeveloped. Furthermore, although various processes for preparing acomposite hydroxide have been also examined, there has not yet beendeveloped a process which enables to prepare in an industrial scale acomposite hydroxide which can sufficiently improve the performance of alithium secondary battery at the present time. Therefore, it has beendesired to develop a process which enables to prepare this compositehydroxide.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2008-147068

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2003-86182

Patent Document 3: Japanese Unexamined Patent Application PublicationNo. Hei 10-214624

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention has been developed in view of the above-mentionedprior arts, and an object of the present invention is to provide nickelcomposite hydroxide particles having a small particle diameter and highuniformity of the particle diameter, and a process which enables toprepare the nickel composite hydroxide particles.

Another object of the present invention is to provide a cathode activematerial for a nonaqueous secondary battery, which enables to decreasethe resistance of a positive electrode when the cathode active materialis used in a battery, and a process for producing the same.

Still another object of the present invention is to provide a nonaqueouselectrolyte secondary battery which is excellent in cyclingcharacteristics, and possesses a high power.

Means for Solving the Problems

(Process for Producing Nickel Composite Hydroxide Particles)

According to the first aspect of the present invention concerning aprocess for producing nickel composite hydroxide particles, there areobtained particles of a nickel composite hydroxide represented by thegeneral formula (I):

Ni_(1-x-y)Co_(x)M_(y)(OH)_(2+α)  (I)

wherein 0≤x≤0.2, 0≤y≤0.15, x+y<0.3, 0≤α≤0.5, and M is at least oneelement selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn,Zr, Nb, Mo and W. This process includes a step for nucleation, whichincludes controlling the pH to 12.0 to 13.4 of an aqueous solution fornucleation containing a metal compound having an atomic ratio of themetal corresponding to the atomic ratio of the metal of the particles ofthe nickel composite oxide and an ammonium ion donor at a liquidtemperature of 25° C., to carry out nucleation, and a step for growth ofparticles, which comprises controlling the pH to 10.5 to 12.0 of theaqueous solution for the growth of particles containing a nucleiobtained in the step for nucleation at a liquid temperature of 25° C.,to grow the nuclei, and the pH in the step for growth of particles iscontrolled so as to be less than the pH in the step for nucleation.

According to the second aspect of the present invention concerning aprocess for producing nickel composite hydroxide particles, after thestep for nucleation is completed in the first aspect of the presentinvention, the pH of the above-mentioned aqueous solution for nucleationis controlled, to form the above-mentioned aqueous solution for nucleigrowth.

According to the third aspect of the present invention concerning aprocess for producing nickel composite hydroxide particles, in the firstaspect of the present invention, an aqueous solution suitable fornucleation is formed, and nuclei formed in the above-mentioned step fornucleation are added to the aqueous solution, to form theabove-mentioned aqueous solution for growth of nuclei.

According to the fourth aspect of the present invention concerning aprocess for producing nickel composite hydroxide particles, in thefirst, second or third aspect of the present invention, after thecompletion of the above-mentioned step for nucleation, a part of liquidportion of the above-mentioned aqueous solution for growth of particlesis discharged, and thereafter, the above-mentioned step for growth ofparticles is carried out.

According to the fifth aspect of the present invention concerning aprocess for producing nickel composite hydroxide particles, in thefirst, second, third or fourth aspect of the present invention, thetemperature of each aqueous solution in the above-mentioned step fornucleation and the above-mentioned step for growth of particles ismaintained to 20° C. or more.

According to the sixth aspect of the present invention concerning aprocess for producing nickel composite hydroxide particles, in thefirst, second, third, fourth or fifth aspect of the present invention,the concentration of ammonium ion is maintained within the range of 3 to25 g/L in the above-mentioned step for nucleation and theabove-mentioned step for growth of particles.

According to the seventh aspect of the present invention concerning aprocess for producing nickel composite hydroxide particles, in thefirst, second, third, fourth or fifth or sixth aspect of the presentinvention, the nickel composite hydroxide obtained in the step forgrowth of particles is covered with a compound having at least oneadditive element mentioned above in its molecule.

(Nickel Composite Hydroxide Particles)

The nickel composite hydroxide particles according to the eighth aspectof the present invention are characterized in that the nickel compositehydroxide particles include the nickel composite hydroxide representedby the general formula (I):

Ni_(1-x-y)Co_(x)M_(y)(OH)_(2+α)  (I)

wherein 0≤x≤0.2; 0≤y≤0.15; x+y<0.3; 0≤α≤0.5; and M is an additiveelement and is at least one element selected from the group consistingof Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W; that the nickelcomposite hydroxide particles are spherical secondary particles formedby the aggregation of plural platelike primary particles; that thesecondary particles have an average particle diameter of 3 to 7 μm; andthat the value of [(d90−d10)/average particle diameter] which is anindex showing the spread of a particle size distribution is 0.55 orless.

The nickel composite hydroxide particles according to the ninth aspectof the present invention are the nickel composite hydroxide particlesaccording to the eighth aspect of the present invention, wherein theabove-mentioned additive element is uniformly distributed in theabove-mentioned secondary particles, and/or the surface of the secondaryparticles are uniformly covered with the additive element.

The nickel composite hydroxide particles according to the tenth aspectof the present invention are the nickel composite hydroxide particlesaccording to the eighth or ninth aspect of the present invention,wherein the nickel composite hydroxide particles are produced by theprocess according to any one of the first to seventh aspects of thepresent invention.

(Process for Producing Cathode Active Material for a NonaqueousElectrolyte Secondary Battery)

A process for producing a cathode active material for a nonaqueouselectrolyte secondary battery according to the eleventh aspect of thepresent invention is a process for producing a cathode active materialincluding a lithium-nickel composite oxide represented by the generalformula (II):

Li_(t)Ni_(1-x-y)Co_(x)M_(y)O₂  (II)

wherein: 0.95≤t≤1.15; 0≤x≤0.2; 0≤y≤0.15; x+y<0.3; and M represents atleast one element selected from the group consisting of Mg, Al, Ca, Ti,V, Cr, Mn, Zr, Nb, Mo and W;wherein the method includes a step for heat-treating the nickelcomposite hydroxide particles according to any one of the eighth totenth aspects of the present invention; a mixing step for mixing alithium compound with the particles after the above-mentionedheat-treatment to form a mixture; and a calcinating step for calcinatingthe mixture formed in the mixing step at a temperature of 700° C. to850° C.

The process for producing the cathode active material for a nonaqueouselectrolyte secondary battery according to the twelfth aspect of thepresent invention is a process according to the eleventh aspect of thepresent invention, wherein the ratio of the number of lithium atomsincluded in the above-mentioned mixture to the sum of the numbers ofmetal atoms other than lithium (number of lithium atoms/sum of thenumbers of metal atoms other than lithium) is controlled to from 0.95/1to 1.15/1.

The process for producing the cathode active material for a nonaqueouselectrolyte secondary battery according to the thirteenth aspect of thepresent invention is a process according to the eleventh or twelfthaspect of the present invention, characterized in that prior to theabove-mentioned calcinating step, precalcination is carried out at atemperature which is less than the temperature of the above-mentionedcalcinating, at which the lithium compound has a reactivity to theparticles after the above-mentioned heat-treatment.

(Cathode Active Material for a Nonaqueous Electrolyte Secondary Battery)

The cathode active material for a nonaqueous electrolyte secondarybattery according to the fourteenth aspect of the present invention is acathode active material includes a lithium-nickel composite oxideconstituted with a lithium-containing composite oxide, represented bythe general formula (II):

Li_(t)Ni_(1-x-y)Co_(x)M_(y)O₂,  (II)

wherein: 0.95≤t≤1.15; 0≤x≤0.2; 0≤y≤0.15; x+y<0.3; and M represents atleast one element selected from the group consisting of Mg, Al, Ca, Ti,V, Cr, Mn, Zr, Nb, Mo and W; which has an average particle diameter of 2to 8 μm, and a value of [(d90−d10)/average particle diameter] which isan index showing the spread of the particle size distribution being 0.60or less.

The cathode active material for a nonaqueous electrolyte secondarybattery according to the fifteenth aspect of the present invention is acathode active material according to the fourteenth invention, which isproduced by the process according to any one of the eleventh, twelfth orthirteenth aspect of the present invention.

(Nonaqueous Electrolyte Secondary Battery)

The nonaqueous electrolyte secondary battery according to the sixteenthaspect of the present invention includes a positive electrode which isformed from the cathode active material for a nonaqueous electrolytesecondary battery according to the fourteenth or fifteenth aspect of thepresent invention.

Effects of the Invention

(Process for Producing Nickel Composite Hydroxide Particles)

According to the first aspect of the present invention, the growth ofnuclei can be suppressed by controlling the pH of an aqueous solutionfor nucleation to 12.0 to 13.4 at its liquid temperature of 25° C., andtherefore, only the nucleation can be substantially carried out in thestep for nucleation. In addition, only the growth of nuclear can bepreferentially carried out by controlling the pH of an aqueous solutionfor growth of particles to 10.5 to 12.0 at a liquid temperature of 25°C., and therefore, the formation of new nuclei can be suppressed. Sincethe nuclei can homogenously grow up in the above processes, uniformnickel composite hydroxide particles having a narrow range of theparticle size distribution can be obtained.

According to the second aspect of the present invention, since theaqueous solution for growth of particles is obtained by controlling thepH of the aqueous solution for nucleation, which is obtained after thecompletion of the step for nucleation, transferring to the step forgrowth of particles can be smoothly carried out.

According to the third aspect of the present invention, since thenucleation can be more distinctly separated from the growth ofparticles, the liquid state in each step can be controlled to the mostsuitable conditions for each step. Therefore, nickel composite hydroxideparticles can be produced so as to have a narrower range of the particlesize distribution and to be uniform.

According to the fourth aspect of the present invention, since theconcentration of the nickel composite hydroxide particle in the aqueoussolution for nucleation can be increased, the particles can grow up inthe state of a higher concentration of the particles. Therefore, theparticle size distribution of the particles can be further narrowed, andthe particle density also can be increased.

According to the fifth aspect of the present invention, since thecontrol of the generation of nuclei can be facilitated, the nucleisuited for producing uniform nickel composite hydroxide particles havinga narrow range of particle size distribution can be formed.

According to the sixth aspect of the present invention, since thesolubility of the metal ions can be controlled to fall within aspecified range, particles having regulated shapes and particlediameters can be formed, and the particle size distribution can be alsonarrowed.

According to the seventh aspect of the present invention, the durabilityand output characteristics of a battery can be improved when the cathodeactive material for a battery, which is formed from the nickel compositehydroxide particles produced by the process according to the presentinvention as a source material, is used in the battery.

(Nickel Composite Hydroxide Particles)

According to the eighth aspect of the present invention, when the nickelcomposite hydroxide particles are mixed with a lithium compound, and theresulting mixture is calcinated, since lithium can be sufficientlydiffused into the nickel composite hydroxide particles, a favorablecathode active material having homogenous distribution of lithium can beobtained. In addition, when the cathode active material is produced fromthe nickel composite hydroxide particles as a source material, thecathode active material can be provided as uniform particles having anarrow range of the particle size distribution. Therefore, when abattery having a positive electrode made of the cathode active materialis formed, the electrode resistance can be reduced, and deterioration ofthe electrode can be suppressed even though charge and discharge arerepeatedly carried out.

According to the ninth aspect of the present invention, when a cathodeactive material for a battery is formed from the nickel compositehydroxide particles of the present invention as a source material, andthe cathode active material is used in a battery, durability and outputcharacteristics of the battery can be improved.

According to the tenth aspect of the present invention, since uniformnickel composite hydroxide particles having a narrow range of theparticle size distribution can be prepared, when a cathode activematerial is produced from the nickel composite hydroxide particles as asource material, the cathode active material can be also produced asuniform particles having a narrow range of the particle sizedistribution. Therefore, when a battery having a positive electrode madeof this cathode active material is formed, since the electroderesistance can be reduced, deterioration of the electrode can beinhibited even though charge and discharge are repeatedly carried out.

(Process for Producing Cathode Active Material for NonaqueousElectrolyte Secondary Battery)

According to the eleventh aspect of the present invention, sinceresidual water in the nickel composite hydroxide particles can beremoved by a heat treatment, the variation of ratio of the number oflithium atoms to the sum of the numbers of metal atoms contained in theproduced lithium-nickel composite oxide can be prevented. Moreover,since calcinating is carried out at a temperature of 750° C. to 850° C.,lithium can be sufficiently diffused in the particles, and the sphericalshape of the particle can be maintained. Therefore, when a batteryhaving a positive electrode formed from the produced cathode activematerial is produced, a battery capacity can be increased, and apositive electrode resistance can be also reduced.

According to the twelfth aspect of the present invention, when apositive electrode is formed by using the obtained cathode activematerial, reaction resistance on the positive electrode can be reduced,and lowering of initial discharge capacity can also be avoided.

According to the thirteenth aspect of the present invention, sincelithium is sufficiently diffused, a uniform lithium-nickel compositeoxide can be obtained.

(Cathode Active Material for Nonaqueous Electrolyte Secondary Battery)

According to the fourteenth aspect of the present invention, when thecathode active material for a nonaqueous electrolyte secondary batteryis used in a battery, high power characteristics and high capacity of abattery can be realized.

According to the fifteenth aspect of the present invention, since thecathode active material is provided as uniform particles having a narrowrange of the particle size distribution, when a battery having apositive electrode made of this cathode active material is formed, theelectrode resistance can be reduced, and deterioration of the electrodecan be suppressed even though charge and discharge are repeatedlycarried out.

(Nonaqueous Electrolyte Secondary Battery)

According to the sixteenth aspect of the present invention, since abattery having a high initial discharge capacity of 180 mAh/g or moreand a low positive electrode resistance is obtained, thermal stabilityand safety can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow chart illustrating the steps for producingthe nickel composite hydroxide of the present invention.

FIG. 2 is a schematic flow chart illustrating other steps for producingthe nickel composite hydroxide of the present invention.

FIG. 3 is a schematic flow chart illustrating the steps for producing alithium-nickel composite oxide from the nickel composite hydroxide ofthe present invention.

FIG. 4 is a schematic flow chart illustrating the steps from theproduction of the nickel composite hydroxide of the present invention tothe production of a nonaqueous electrolyte secondary battery.

FIG. 5 is a table showing the results of Examples and ComparativeExamples.

FIG. 6 is an SEM photograph (magnification: 1,000) of the nickelcomposite hydroxide of the present invention.

FIG. 7 is an SEM photograph (magnification: 1,000) of the lithium-nickelcomposite oxide of the present invention.

FIG. 8 is a schematic cross sectional view illustrating a coin-typebattery which was used for evaluating a battery.

FIG. 9 is a schematic explanatory drawing illustrating an example ofmeasurement for the evaluation of impedance and an equivalent circuitwhich was used for analysis.

MODE FOR CARRYING OUT THE INVENTION

As above-mentioned, the present invention relates to (1) a nonaqueouselectrolyte secondary battery; (2) a cathode active material for anonaqueous electrolyte secondary battery used in a positive electrode ofthe nonaqueous electrolyte secondary battery and a process for producingthe same; (3) nickel composite hydroxide particles which are used as asource material of the cathode active material for a nonaqueouselectrolyte secondary battery and a process for producing the same.

In order to improve the performance of a nonaqueous electrolytesecondary battery, there is a necessity to use an electrode in which acathode active material for a nonaqueous electrolyte secondary batterywhich is excellent in battery characteristics. In order to obtain acathode active material for a nonaqueous electrolyte secondary batterywhich is excellent in battery characteristics, the particle diameter andparticle size distribution thereof are important factors, and a cathodeactive material having a desired particle diameter and being regulatedto have a desired particle size distribution is preferred. In order toobtain the cathode active material, there is a necessity to use nickelcomposite hydroxide particles having a desired particle diameter and adesired particle size distribution as a source material thereof.

As above-mentioned, the present invention relates to a process forproducing nickel composite hydroxide particles having a narrow range ofthe particle size distribution which affects the performance of a finalproduct, a nonaqueous electrolyte secondary battery and a nickelcomposite hydroxide particles produced by this method.

In addition, the aspect of the present invention also involves a processfor producing a cathode active material for a nonaqueous electrolytesecondary battery having a desired particle diameter and being regulatedto have a desired particle size distribution, in which the uniformnickel composite hydroxide particles having a narrow range of theparticle size distribution produced by the above-mentioned process isused as a source material, and the cathode active material for anonaqueous electrolyte secondary battery which is produced by thismethod are also involved in aspects of the present invention.Furthermore, the aspect of the present invention also involves anonaqueous electrolyte secondary battery having a positive electrodeproduced by the process according to the present invention, in which thecathode active material for a nonaqueous electrolyte secondary batteryhaving a desired particle diameter and being regulated to have a desiredparticle size distribution is used.

The present invention will be specifically described hereinafter. Priorto the description of a process for producing nickel composite hydroxideparticles and nickel composite hydroxide particles, which are thegreatest characteristics of the present invention, hereinafter aredescribed a nonaqueous electrolyte secondary battery which is a finalproduct; a process for producing a cathode active material for anonaqueous electrolyte secondary battery in which nickel compositehydroxide particles are used as a source material; and the cathodeactive material for a nonaqueous electrolyte secondary battery.

(1) Nonaqueous Electrolyte Secondary Battery

The nonaqueous electrolyte secondary battery of the present inventionhas a positive electrode formed from a cathode active material for anonaqueous electrolyte secondary battery (2) which is described later asshown in FIG. 4. Since the positive electrode is used in the nonaqueouselectrolyte secondary battery of the present invention, the battery hasa high initial discharge capacity of 180 mAh/g or more and a lowpositive electrode resistance, and is excellent in thermal stability andsafety.

First of all, the structure of a nonaqueous electrolyte secondarybattery of the present invention is explained.

The nonaqueous electrolyte secondary battery of the present invention(hereinafter, simply referred to as “secondary battery of the presentinvention”) has a structure substantially the same as the structure ofusual nonaqueous electrolyte secondary batteries, except that thecathode active material for a nonaqueous electrolyte secondary batteryaccording to the present invention (hereinafter, simply referred to as“cathode active material of the present invention”) is used as amaterial of the positive electrode.

Specifically, the secondary battery of the present invention is providedwith a case, a positive electrode, a negative electrode, a nonaqueouselectrolytic solution and a separator which are accommodated in thiscase. More specifically, the secondary battery of the present inventionis formed by laminating a positive electrode with a negative electrodevia a separator to form an electrode assembly, impregnating a nonaqueouselectrolytic solution into the obtained electrode assembly, connecting apositive electrode collector of the positive electrode with a positiveelectrode terminal which is communicated with an exterior, and anegative electrode collector of a negative electrode with a negativeelectrode terminal which is communicated with the exterior by using alead for power collection or the like respectively, and closing thecase. Incidentally, the structure of the secondary battery of thepresent invention is not limited to the above-mentioned exemplifiedones, and various external forms such as a cylindrical shape and alaminated layer structure can be employed.

(Structure of Each Part)

Next, the structure of each part used in the secondary battery of thepresent invention is explained.

(Positive Electrode)

First of all, the positive electrode which is one of the characteristicsof the secondary battery of the present invention is described below.

The positive electrode is a sheet material, and is formed by coating apaste for forming a positive electrode, which contains the cathodeactive material of the present invention on, for example, the surface ofa collector made of an aluminum foil, and drying the paste.

Incidentally, the positive electrode is appropriately processed to meetthe battery used. For example, a cutting processing for forming into anappropriate size in accordance with the size of a battery intended, acompression processing such as roll pressing for increasing electrodedensity and the like are carried out.

(Positive Electrode Mixture Paste)

The paste for forming a positive electrode is obtained by adding asolvent to the positive electrode mixture, followed by kneading. Inaddition, the positive electrode mixture is obtained by mixing thepowdery cathode active material of the present invention, anelectrically conductive material and a binder.

The electrically conductive material is used in order to impart adequateelectric conductivity to an electrode. The electrically conductivematerial is not particularly limited, and there can be cited, forexample, carbon blacks such as graphite (natural graphite, artificialgraphite, expanded graphite and the like), acetylene black and Ketjenblack; and the like.

The binder plays a role in binding the cathode active materialparticles. The binder for use in the positive electrode mixture is notparticularly limited, and there can be cited, for example,polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinerubber, ethylene-propylene-diene rubber (EPR), styrene-butadiene rubber(SBR), cellulose, polyacrylic acid, and the like.

Incidentally, to the positive electrode mixture may be added anactivated carbon, and the like. The electric double layer capacity ofthe positive electrode can be increased by adding the activated carbonand the like.

The solvent is used in order to dissolve the binder, and disperse acathode active material, an electrically conductive material, activatedcarbon and the like in the binder. This solvent is not particularlylimited, and there can be cited, for example, an organic solvent such asN-methyl-2-pyrrolidone.

In addition, the mixing ratio of each substance used in the paste forforming a positive electrode is not particularly limited. For example,based on 100 parts by mass of solids of the positive electrode mixturefrom which a solvent is removed, the amount of the cathode activematerial can be 60 to 95 parts by mass, the amount of the electricallyconductive material can be 1 to 20 parts by mass, and the amount of thebinder can be 1 to 20 parts by mass, in the same manner as in the usualpositive electrodes of nonaqueous electrolyte secondary batteries.

(Negative Electrode)

The negative electrode is a sheet material formed by coating a paste forforming a negative electrode on the surface of a foil collector of ametal such as copper, and drying the paste. The components whichconstitute the paste for forming a negative electrode and a material ofa collector used in this negative electrode are different from thoseused in the positive electrode. This negative electrode can be formed inthe substantially same manner as in the positive electrode as describedabove. As occasion demands, various treatments are applied to thenegative electrode as well as the positive electrode.

The paste for forming a negative electrode is prepared by adding asuitable solvent to a negative electrode mixture which is prepared bymixing a anode active material with a binder, to form a paste.

As the anode active material, there can be used, for example, alithium-containing material such as metal lithium or a lithium alloy, ora storage substance capable of storing and desorbing lithium ions.

The storage substance is not particularly limited, and there can becited, for example, natural graphite, artificial graphite, calcinatedproducts of an organic compound such as a phenol resin, and powderymatter of a carbon substance such as coke, and the like. When thestorage substance is used in the anode active material, afluorocarbon-containing resin such as polyvinylidene fluoride (PVDF) canbe used as a binder as well as the positive electrode. In order todisperse the anode active material in the binder, a solvent can be used.The solvent includes, for example, an organic solvent such asN-methyl-2-pyrrolidone.

(Separator)

A separator is disposed to be sandwiched between the positive electrodeand the negative electrode. The separator has a function for separatingthe positive electrode from the negative electrode and a function forretaining the electrolyte. As the separator, there can be used a thinmembrane made of, for example, polyethylene or polypropylene, and havingmany fine pores. However, the separator is not particularly limitedthereto as long as the separator has the above-mentioned functions.

(Nonaqueous Electrolytic Solution)

The nonaqueous electrolytic solution is prepared by dissolving a lithiumsalt as a supporting salt in an organic solvent.

The organic solvent includes, for example, cyclic carbonates such asethylene carbonate, propylene carbonate, butylene carbonate andtrifluoropropylene carbonate; chain carbonates such as diethylcarbonate, dimethyl carbonate, ethylmethyl carbonate and dipropylcarbonate; ether compounds such as tetrahydrofuran,2-methyltetrahydrofuran and dimethoxyethane; sulfur compounds such asethylmethylsulfone and butanesulfone; phosphorus compounds such astriethyl phosphate and trioctyl phosphate; and the like. The presentinvention is not limited to those exemplified ones. These organiccompounds may be used alone, or may be used by mixing at least two kindsthereof.

As the supporting salt, there can be cited, for example, LiPF₆, LiBF₄,LiClO₄, LiAsF₆, LiN(CF₃SO₂)₂, and composite salts thereof.

Incidentally, the nonaqueous electrolytic solution may contain a radicalscavenger, a surface active agent, a fire retardant and the like inorder to improve the characteristics of a battery.

(Characteristics of Secondary Battery of the Present Invention)

Since the secondary battery of the present invention has theabove-mentioned constituents, and the above-mentioned positive electrodeis used therein, the secondary battery has a high capacity and a highpower, as well as a high initial discharge capacity of 180 mAh/g or moreand a low positive electrode resistance. Moreover, the secondary batteryis excellent in thermal stability and safety in comparison withconventional cathode active materials made of lithium nickel oxide.

(Uses of a Secondary Battery of the Present Invention)

Since the secondary battery of the present invention has theabove-mentioned properties, the secondary battery can be used as anelectric power supply for a small size mobile electronic device whichalways requires a high capacity (notebook-sized personal computer,mobile phone terminal, and the like). In addition, the secondary batteryof the present invention is also suitably used as a battery for anelectric automobile which requires a high power. When a battery for anelectric automobile has a larger size, ensuring of safety will bedifficult, and an expensive protective circuit will be essential. Incontrast, since the secondary battery of the present invention hasexcellent safety without increasing in size of a battery, not onlyensuring of safety is facilitated, but also an expensive protectivecircuit can be simplified, and cost can be more reduced. In addition,since the secondary battery can be miniaturized and provide a higheroutput, the secondary battery can be suitably used as an electric powersupply for an electric automobile which is restricted by a mountingspace. The secondary battery of the present invention can be also usednot only as an electric power supply for an electric automobile which isdriven only by electric energy but also as an electric power supply fora so-called hybrid automobile in which a combustion engine such as agasoline engine or a diesel engine is used in combination.

(2) Cathode Active Material for Nonaqueous Electrolyte Secondary Battery

The cathode active material for a nonaqueous electrolyte secondarybattery according to the present invention (hereinafter, referred to as“cathode active material of the present invention”) is suited for amaterial of a positive electrode of a nonaqueous electrolyte secondarybattery as described above.

The cathode active material of the present invention includeslithium-nickel composite oxide particles represented by the generalformula (II):

Li_(t)Ni_(1-x-y)Co_(x)M_(y)O₂,  (II)

wherein 0.95≤t≤1.15, 0≤x≤0.2, 0≤y≤0.15, x+y<0.3, and M is at least oneelement selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn,Zr, Nb, Mo and W.

The crystal structure of the cathode active material of the presentinvention is not particularly limited. It is preferred that the crystalstructure is a hexagonal crystal structure having a layer structurebased upon the lithium-nickel composite oxide which has been usuallyused as a cathode active material.

(Particle Size Distribution)

The cathode active material of the present invention is controlled sothat [(d90−d10)/average particle diameter] which is an index showing aspread of the particle size distribution has 0.6 or less.

When the particle size distribution has a broader range, there existmany fine particles having a particle diameter very smaller than itsaverage particle diameter, or many particles having a particle diametervery larger than its average particle diameter (large particles) in thecathode active material. When a positive electrode is formed by using acathode active material in which many fine particles exist, safety willbe lowered since the fine particles generate heat due to its localreaction, and cycle characteristics will be lowered since the fineparticles selectively deteriorate due to the heat. On the other hand,when a positive electrode is formed by using a cathode active materialin which many large particles exist, since the area where theelectrolytic solution is reacted with the cathode active materialbecomes insufficient, reaction resistance is increased, and therefore,the output of a battery is lowered.

In contrast, according to the present invention, since the value of[(d90−d10)/average particle diameter] which shows the spread of aparticle size distribution of the cathode active material is controlledso that the value is 0.6 or less, the ratio of the fine particles andthe large particles becomes lower, and therefore, a battery in whichthis cathode active material is used in the positive electrode isexcellent in safety and has favorable cycle characteristics and batteryoutput.

In addition, it is advantageous that the value of [(d90−d10)/averageparticle diameter] showing the spread of particle size distribution ofthe cathode active material is smaller from the viewpoint of improvementin performance of the cathode active material, and it is preferred thatits lower limit is about 0.05 as to the cathode active material obtainedin the present invention.

Incidentally, in the index of [(d90−d10)/average particle diameter],“d10” means a particle diameter at which an accumulated volume is 10% ofthe total volume of all particles when the numbers of particles having aspecified particle diameter are accumulated from particles having asmaller particle diameter. Also, “d90” means a particle diameter atwhich an accumulated volume is 90% of the total volume of all particleswhen the numbers of particles having a specified particle diameter areaccumulated from particles having a smaller particle diameter.

Methods for determining the average particle diameter, the value of“d90” and the value of “d10” are not particularly limited. The averageparticle diameter, the value of “d90” and the value of “d10” can bedetermined from, for example, volume-integrated values as measured bymeans of a laser diffraction scattering type particle size analyzer.

(Average Particle Diameter)

The particle diameter of the cathode active material of the presentinvention is from 2 to 8 μm, preferably from 3 to 8 μm, more preferablyfrom 3 to 6 μm. When the average particle diameter is less than 2 μm,packing density of the battery capacity per volume of the positiveelectrode is lowered. When the average particle diameter exceeds 8 μm,since the specific surface area of the cathode active material islowered, the area where the cathode active material is contacted withthe electrolytic solution of a battery is decreased, and therefore, theresistance of the positive electrode is increased, and the outputcharacteristics of a battery is lowered.

Accordingly, a battery in which the cathode active material of thepresent invention is used in the positive electrode has a large batterycapacity per its volume, and also has excellent battery characteristicssuch as high safety and high power.

(Composition of Particles)

In the cathode active material of the present invention, the atomicratio of lithium is within a range of from 0.95 to 1.15 in theabove-mentioned general formula (II). When the ratio of lithium issmaller than the above-mentioned range, since the reaction resistance ofthe positive electrode increases in the nonaqueous electrolyte secondarybattery in which the cathode active material is used, the output of thebattery is lowered. When the ratio “t” of lithium is larger than theabove-mentioned range, the reaction resistance of the positive electrodeincreases, as well as the initial discharge capacity of the cathodeactive material is lowered. It is more preferred that the atomic ratio“t” of lithium is from 1.0 to 1.15.

In addition, in the cathode active material of the present invention,cobalt may not be existed. However, in order to obtain better cyclecharacteristics, it is preferred that cobalt is contained in the cathodeactive material since expansion-contraction behavior of the crystallattice, which is caused by the desorption or insertion of Liaccompanying with charge and discharge can be reduced by substituting apart of Ni existing in the crystal lattice with cobalt. From theviewpoint as mentioned above, the atomic ratio “x” of cobalt is from 0to 0.2, preferably from 0.08 to 0.2, and more preferably from 0.12 to0.20. In addition, from the viewpoint of battery capacity and outputcharacteristics, the atomic ratio of nickel to cobalt (Ni/Co) ispreferably from 0.75/0.25 to 0.9/0.1, more preferably from 0.8/0.2 to0.85/0.15, and particularly preferably 0.82/0.15.

In addition, as represented by the above-mentioned general formula (II),it is preferred that the cathode active material of the presentinvention contains an additive element since durability and outputcharacteristics of a battery can be improved when the cathode activematerial of the present invention is used in the battery.

Moreover, it is preferred that the additive element is homogenouslydistributed on the surface or inside of the lithium-nickel compositeoxide particles since lowering of the capacity can be inhibited, as wellas durability characteristics and output characteristics of a batterycan be improved in a small amount. Also, in order to be able to improvedurability characteristics and output characteristics of a battery in asmaller amount and to inhibit the lowering of capacity, it is preferredthat the amount of the additive element on the surface of thelithium-nickel composite oxide particles is greater than the amount ofthe additive element inside the lithium-nickel composite oxideparticles.

Incidentally, it is not preferred that the atomic ratio “y” of theadditive element “M” exceeds 0.15 since the metal elements whichcontribute to a Redox reaction decrease, and thereby battery capacity islowered. Therefore, the lower limit of the atomic ratio “y” of theadditive element “M” is 0, and preferably 0.001 or more from theviewpoint of inhibition of lowering of capacity as well as improvementin durability characteristics and output characteristics of a battery ina smaller amount.

(Process for Producing Cathode Active Material for NonaqueousElectrolyte Secondary Battery)

The process for producing a cathode active material of the presentinvention is not particularly limited so long as a cathode activematerial can be produced so as to have the above-mentioned crystalstructure, average particle diameter, particle size distribution andcomposition. It is preferred that the following process is employedsince the cathode active material of the present invention can beproduced more certainly.

As shown in FIG. 3, the process for producing a cathode active materialof the present invention includes (a) a step for heat-treating nickelcomposite hydroxide particles which are used as a source material of acathode active material of the present invention, (b) a mixing step formixing the particles after the above-mentioned heat-treatment with alithium compound to form a mixture, and (c) a calcinating step forcalcinating the mixture formed in the above-mentioned mixing step. Thelithium-nickel composite oxide particles, that is, the cathode activematerial of the present invention can be obtained by pulverizing thesintered product.

The “pulverizing” means that a mechanical energy is applied to theaggregates including plural secondary particles, which are generated bysinter-necking or the like between the secondary particles duringcalcinating, to separating the secondary particles with each other withscarcely breaking of the secondary particles to loosen the aggregates.

Each step will be described below:

(a) Heat Treatment Step

The heat treatment step is a step for heating nickel composite hydroxideparticles (hereinafter, simply referred to as composite hydroxideparticles) to carry out a heat treatment, to remove moisture containedin the composite hydroxide particles. By carrying out this heattreatment step, the moisture contained in the composite hydroxideparticles, which remains until a calcinating step can be reduced. Inother words, since the composite hydroxide particles can be convertedinto composite oxide particles by this heat treatment step, the numberof metal atoms and the ratio of the number of lithium atoms in theproduced cathode active material can be prevented from variation.

Incidentally, there is no necessity to convert all of the compositehydroxide particles into composite oxide particles, since moisture hasonly to be removed to an extent which does not cause the variation ofthe number of atoms of metals and the ratio of the number of lithiumatoms in the cathode active material.

In the heat treatment step, the composite hydroxide particles can beheated up to a temperature which enables to remove residual moisture.The temperature of the heat treatment is not particularly limited, andit is preferred that the temperature is 105° C. to 800° C. For example,when the composite hydroxide particles are heated to 105° C. or more,the residual moisture can be removed. Also, when the temperature of theheat treatment is less than 105° C., it tends to necessitate a longerperiod of time for removing the residual moisture. When the temperatureof the heat treatment exceeds 800° C., the particles being convertedinto composite oxide may be aggregated by calcining.

When the heat treatment of the composite hydroxide particles is carriedout, the atmosphere is not particularly limited, and the air isfavorable since the heat treatment can be conveniently carried out.

In addition, the time period of the heat treatment for the compositehydroxide particles cannot be absolutely determined since the timeperiod differs depending on the temperature during the heat treatment.The time period is preferably 1 hour or more, more preferably 5 to 15hours since there is a possibility that the removal of residual moisturein the composite hydroxide particles cannot be sufficiently carried outwhen the time period is less than 1 hour. The equipment which is used inthe heat treatment is not particularly limited, and any equipment whichenables the composite hydroxide particles to be heated in the airflow isacceptable. There can be cited as the equipment, for example, an airdryer, an electric furnace which does not generate gas, and the like.

(b) Mixing Step

The mixing step is a step for mixing the particles obtained byheat-treating the composite hydroxide particles in the heat treatmentstep (hereinafter, referred to as heat treated particles) with a lithiumcompound, to give a lithium mixture.

Incidentally, the heat treated particles means nickel compositehydroxide particles from which residual moisture has been removed in theheat treatment step, nickel composite oxide particles which have beenconverted into oxide in the heat treatment step, or mixed particlesthereof.

The ratio of the number of lithium atoms (Li) in the lithium mixture tothe number of atoms of the metals other than lithium, that is, the sumof the number of the atoms of nickel, cobalt and additive elements (Me)(hereinafter, referred to as “Li/Me”) is preferably from 0.95/1 to1.15/1, more preferably from 1/1 to 1.1/1. More specifically, the mixingis carried out so that the ratio of Li/Me in the lithium mixture becomesthe same as the ratio of Li/Me in the cathode active material of thepresent invention. This is because the ratio of Li/Me in this mixingstep corresponds to the ratio of Li/Me in the cathode active material,since the Li/Me is unchanged before and after the calcining step.

Accordingly, the lithium compound is mixed with the heat-treatedparticles so that the ratio of Li/Me can be preferably from 0.95/1 to1.15/1, more preferably from 1/1 to 1.1/1.

It is preferred that the lithium compound which is used for theformation of the lithium mixture is lithium hydroxide, lithium nitrate,lithium carbonate or a mixture thereof since they are readily available.In addition, from the viewpoint of facility of handling and stability ofquality, lithium hydroxide is more preferable.

Incidentally, it is preferred that the lithium mixture is sufficientlymixed prior to calcinating. When the mixing is not sufficiently carriedout, the variation of Li/Me will be caused between each particle, andtherefore, there is a possibility that sufficient batterycharacteristics cannot be obtained.

When carrying out mixing, a conventional mixer can be used. There can becited as the mixer, for example, a shaker mixer, Loedige mixer, JULIAmixer, V blender, and the like. The heat treated particles can besufficiently mixed with a substance which contains lithium to an extentsuch that the external shape of the composite hydroxide particles is notdestroyed.

(c) Calcinating Step

The calcinating step is a step for calcinating the lithium mixtureobtained in the above-mentioned mixing step, to form a lithium-nickelcomposite oxide. When the lithium mixture is calcinated in thecalcinating step, since lithium in the substance containing lithium isdiffused in the heat treated particles, the lithium-nickel compositeoxide is formed.

(Calcinating Temperature)

The calcinating temperature of the lithium mixture is from 700° C. to850° C., preferably from 720° C. to 820° C.

When the calcinating temperature is less than 700° C., lithium is notsufficiently diffused in the heat treated particles. Therefore,excessive lithium and unreacted particles remain in the lithium mixture,and the crystal structure is not satisfactorily regulated, wherebysufficient battery characteristics cannot be obtained. On the otherhand, when the calcinating temperature exceeds 850° C., there is apossibility that calcining will drastically occur between the heattreated particles, and that abnormal particles will be generated.Accordingly, there is a possibility that the shape of particles (shapeof spherical secondary particles as described later) cannot bemaintained since the particles become coarse when calcinating.Therefore, when a cathode active material is formed from the particles,a specific surface area will be lowered, thereby the resistance of apositive electrode will increase, and the capacity of a battery will belowered.

(Calcinating Period of Time)

The calcinating period of time is preferably 3 hours or more, morepreferably 6 to 24 hours. When the calcinating period of time period isless than 3 hours, there is a possibility that the generation of alithium-nickel composite oxide is not sufficiently carried out.

(Precalcination)

When a lithium hydroxide, lithium carbonate or the like is used as thelithium compound, prior to the calcining at a temperature of 700° C. to850° C., it is preferred that preheating is carried out at a temperatureless than the calcining temperature and a temperature at which thelithium compound can be reacted with the heat-treated particles. Whenthe lithium mixture is maintained at the temperature, lithium issufficiently diffused in the heat treated particles, and thereby auniform lithium-nickel composite oxide can be obtained. For example,when a lithium hydroxide is used, it is preferred that the preheating iscarried out with maintaining the temperature at 400° C. to 550° C. for 1to 10 hours or so.

As described above, when the concentration of the additive element “M”increases on the surface of the lithium-nickel composite oxideparticles, the heat treated particles which are homogenously coveredwith the additive element on their surfaces can be used. Theconcentration of the additive element on the surface of theabove-mentioned composite oxide particles can be increased bycalcinating the lithium mixture containing the heat treated particlesunder appropriate conditions. More specifically, when the lithiummixture containing the heat treated particles covered with the additiveelement is calcinated at a lower calcinating temperature for a shortercalcinating period of time, lithium-nickel composite oxide particleshaving an increased concentration of the additive element “M” on thesurface of the particles can be obtained.

When the lithium mixture containing the heat treated particles coveredwith the additive element is calcinated at a higher calcinatingtemperature for a longer calcinating period of time, lithium-nickelcomposite oxide particles having the additive element homogenouslydistributed in the particles can be obtained. In other words, intendedlithium-nickel composite oxide particles can be obtained by controllingthe components of the heat treated particles and calcinating conditions.

(Calcinating Atmosphere)

When calcinating is carried out, the atmosphere is preferably anoxidizable atmosphere, more preferably an atmosphere having an oxygenconcentration of 18 to 100% by volume. When the oxygen concentration isless than 18% by volume, the nickel composite hydroxide particlescontained in the heat treated particles cannot be sufficiently oxidized,and therefore, there is a possibility such that the crystallinity of thelithium-nickel composite oxide becomes insufficient. Accordingly, it ispreferred that the calcinating of the lithium mixture is carried out inthe air or in an oxygen flow. In consideration of the batterycharacteristics, it is preferred that the lithium mixture is calcinatedin the oxygen stream.

The furnace used in the calcinating is not particularly limited, and anyfurnace which enables the lithium mixture to be heated in the air or inan oxygen flow can be used. Among the furnaces, an electric furnacewhich does not generate gas is preferred, and either a batch typefurnace or a continuous type furnace can be used.

(3) Nickel Composite Hydroxide Particles

The nickel composite hydroxide, which is used in the nickel compositehydroxide particles of the present invention (hereinafter, simplyreferred to as “composite hydroxide particles of the presentinvention”), is represented by the general formula (I):

Ni_(1-x-y)Co_(x)M_(y)(OH)_(2+α)  (I)

wherein 0≤x 0.2, 0≤y≤0.15, x+y<0.3; 0≤α≤0.5, and M is at least oneadditive element selected from the group consisting of Mg, Al, Ca, Ti,V, Cr, Mn, Zr, Nb, Mo and W. The composite hydroxide particles of thepresent invention are spherical secondary particle formed by theaggregation of plural platelike primary particles. The secondaryparticles are ones which have an average particle diameter of 3 to 7 μm,and the index of [(d90−d10)/average particle diameter], which shows thespread of the particle size distribution, being 0.55 or less.

The composite hydroxide particles of the present invention areparticularly suitable as a source material of the above-mentionedcathode active material of the present invention. Therefore, thecomposite hydroxide particles of the present invention are describedbelow on the premise of the use of the composite hydroxide particles asa source material of the cathode active material of the presentinvention.

(Particle Structure)

The composite hydroxide particles of the present invention are sphericalparticles, and more specifically spherical secondary particles which areformed by the aggregation of plural platelike primary particles. Sincethe composite hydroxide particles of the present invention have theabove structure, lithium is sufficiently distributed in the heat treatedparticles in the above-mentioned calcinating step for forming thecathode active material of the present invention. Therefore, a favorablecathode active material having a uniform distribution of lithium isobtained.

It is preferred that the composite hydroxide particles of the presentinvention are ones which are formed by the aggregation of platelikeprimary particles in random directions. When the platelike primaryparticles are aggregated in random directions, voids are approximatelyuniformly formed between each primary particle. Therefore, when theprimary particles are mixed with the lithium compound, and thencalcinated, since the molten lithium compound distributes over thesecondary particles, the diffusion of lithium is sufficiently carriedout.

(Particle Size Distribution)

In the composite hydroxide particles of the present invention, the indexof [(d90−d10)/average particle diameter] which shows the spread ofparticle size distribution is controlled to 0.55 or less. Since theparticle size distribution of the cathode active material issignificantly affected by the composite hydroxide particles which areused as a source material, when fine particles or coarse particles arecontained in the composite hydroxide particles, particles similar tothose particles are also existed in the cathode active material.Accordingly, the value of [(d90−d10)/average particle diameter] exceeds0.55, and fine particles or coarse particles are also existed in thecathode active material. In the composite hydroxide particles of thepresent invention, since the value of [(d90−d10)/average particlediameter] is controlled to 0.55 or less, the particle size distributionof the cathode active material, which is prepared by using the compositehydroxide particles of the present invention as a source material, isnarrowed, and therefore, its particle diameter is regulated. Therefore,the index of [(d90−d10)/average particle diameter] of the cathode activematerial being obtained can be controlled to 0.55 or less. Thereby,favorable cycle characteristics and output can be imparted to a batteryhaving an electrode formed from the cathode active material which isprepared by using the composite hydroxide particles of the presentinvention as a source material.

(Average Particle Diameter)

The average particle diameter of the composite hydroxide particles ofthe present invention is 3 to 7 μm. Since the average particle diameterof the composite hydroxide particles of the present invention is 3 to 7μm, the cathode active material, which is prepared by using thecomposite hydroxide particles of the present invention as a sourcematerial, usually has a given average particle diameter of 2 to 8 μm.When the average particle diameter of the composite hydroxide particlesof the present invention is less than 3 μm, the average particlediameter of the cathode active material becomes small, and the packingdensity of a positive electrode is lowered. Therefore, the capacity of abattery per volume is lowered. On the other hand, when the averageparticle diameter of the composite hydroxide particles of the presentinvention exceeds 7 μm, since the specific surface area of the cathodeactive material is lowered, and the area where the cathode activematerial is contacted with the electrolytic solution is decreased, theresistance of the positive electrode is increased, to result in loweringof output characteristics of a battery. Since the composite hydroxideparticles of the present invention have a given average particlediameter, a battery having a positive electrode formed by using thecathode active material of the present invention, which is prepared byusing the composite hydroxide particles of the present invention as asource material, has excellent battery characteristics.

(Composition of Particles)

The nickel composite hydroxide particles which are used in the compositehydroxide particles of the present invention have a compositionrepresented by the general formula (I). Therefore, a nickel compositehydroxide suited for a source material for producing a lithium-nickelcomposite oxide, which is a cathode active material, can be formed byusing the composite hydroxide particles of the present invention.Moreover, when a lithium-nickel composite oxide is prepared by usingthis nickel composite hydroxide as a source material, and an electrodeof which cathode active material is this lithium-nickel composite oxideis used in a battery, since the resistance of the positive electrode asdetermined can be lowered, output characteristics of the battery can beimproved.

In addition, when a cathode active material is prepared by theabove-mentioned process, the composition ratio (Ni:Co:M) of thecomposite hydroxide particles of the present invention is alsomaintained in the cathode active material.

Accordingly, it is preferred that the composition ratio of the compositehydroxide particles of the present invention is controlled so that thecomposition ratio becomes the same as that of an intended cathode activematerial.

(Process for Producing Nickel Composite Hydroxide Particles)

The process for producing composite hydroxide particles of the presentinvention includes

(a) a step for nucleation, which includes controlling the pH of anaqueous solution for nucleation containing a metal compound having anatomic ratio of metals corresponding to the atomic ratio of the metalsin the nickel composite oxide particles and an ammonium ion donor to12.0 to 13.4 at a liquid temperature of 25° C., to carry out nucleation,and(b) a step for growth of particles for growing the nuclei, whichincludes controlling the pH of the aqueous solution for growth ofparticles containing the nuclei obtained in the step for nucleation to10.5 to 12.0 at a liquid temperature of 25° C.

In the process for producing composite hydroxide particles of thepresent invention, there is a characteristic in that the time at whichthe nucleation reaction is mainly carried out (a step for nucleation) isdistinctly separated from the time at which the particle growth reactionis mainly carried out (step for growth of particles), although accordingto the conventional continuous crystallization method (see PatentDocuments 2 and 3), the nucleation reaction is carried out at the sametime of the particle growth reaction in the same vessel.

First of all, summary of the process for producing composite hydroxideparticles of the present invention is explained below with reference toFIG. 1. Incidentally, in FIG. 1 and FIG. 2, the step (A) corresponds tothe step for nucleation, and the step (B) corresponds to the step forgrowth of particles.

(Nucleation Step)

In the nucleation step as shown in FIG. 1, a solution for nucleationcontaining a metal compound having an atomic ratio of a metalcorresponding to the atomic ratio of a metal in the particles of nickelcomposite hydroxide represented by the general formula (I) and anammonium ion donor is prepared, to generate nuclei in this solution fornucleation. This solution for nucleation is prepared by mixing a mixedaqueous solution with an aqueous solution before reaction.

At first, as shown in FIG. 1, the mixed aqueous solution is prepared bydissolving plural metal compounds containing nickel in water in aspecified ratio. At that time, the ratio of the metal compound which isdissolved in water is controlled so that the atomic ratio of each metalin the mixed aqueous solution becomes the same atomic ratio of metals inthe particles of the nickel composite oxide represented by the generalformula (I), to prepare a mixed aqueous solution.

On the other hand, the aqueous solution before reaction is prepared bysupplying an aqueous alkali solution such as an aqueous sodium hydroxidesolution, an aqueous ammonia solution containing an ammonium ion donorand water to a reaction vessel, and mixing them.

The pH of the aqueous solution is controlled to a range of 12.0 to 13.4at a liquid temperature of 25° C. by adjusting the amount of an aqueousalkali solution being supplied. At the same time, the concentration ofammonium ion in the aqueous solution before reaction is controlled to 3to 25 g/L. Also, the temperature of the aqueous solution before reactionis controlled to 20 to 60° C.

While stirring the aqueous solution before reaction of which temperatureand pH are controlled in a reaction vessel, the above-mentioned mixedaqueous solution is supplied to the reaction vessel. As mentioned above,since the pH of the aqueous solution before reaction is controlled to arange of 12.0 to 13.4 at a liquid temperature of 25° C., when theaqueous solution before reaction is mixed with the mixed aqueoussolution, an aqueous solution for nucleation is formed. Therefore, finenuclei of the composite hydroxide are generated. At that time, since thepH of the aqueous solution for nucleation is within the above-mentionedrange, the generated nuclei little grow, and the formation of nuclei isadvantageously occurs.

Incidentally, during the formation of the nuclei, since the pH andconcentration of ammonium ion of the aqueous solution for nucleation ischanged, the mixed aqueous solution, the aqueous alkali solution and theaqueous ammonia solution are supplied to the aqueous reaction solutionfor nucleation, and thereby, the pH and the concentration of ammoniumion of the aqueous reaction solution for nucleation are maintained at adesignated value.

As described in the above, when the mixed aqueous solution, the aqueousalkali solution and the aqueous ammonia solution are successivelysupplied to the aqueous solution for nucleation, new nuclei aresuccessively and continuously generated in the aqueous solution fornucleation.

Subsequently, when the nuclei are produced in a specified amount in theaqueous solution for nucleation, the step for nucleation is terminated.Whether or not the nuclei are formed in a predetermined amount can bedecided by the amount of the metal compound being added to the aqueoussolution for nucleation.

(Particle Growth Step)

After the step for nucleation is completed, nuclei, which are generatedin the step for nucleation, are grown up in an aqueous solution forgrowth of particles, the pH of which is controlled to 10.5 to 12.0 at aliquid temperature of 25° C. The aqueous solution for growth ofparticles can be obtained by supplying the aqueous solution for growthof particles after the step for nucleation with an acid or a metal saltsolution, to control the pH to 10.5 to 12.0. One of characteristics ofthe present invention also resides in that the pH of the aqueoussolution for growth of particles is controlled to a regulated range.

In the aqueous solution for growth of particles having a pH of 12.0 orless, the reaction for growth of nuclei is more advantageously proceededthan the reaction for generation of nuclei. Therefore, new nuclei wouldbe little generated in the aqueous solution for growth of particles.When composite hydroxide particles having a specified particle diameterare generated in a specified amount, the step for growth of particles isterminated. The amount of the generated composite hydroxide particleshaving a specified particle diameter is determined by the amount of themetal compound which is added to the aqueous solution for nucleation.

As described in the above, according to the process for producing thecomposite hydroxide particles, nucleation preferentially occurs in thecourse of the step for nucleation, and the growth of nuclei littleoccurs in the course of the step for nucleation. In contrast, in thecourse of the step for growth of particles, only the growth of particlesoccurs, and new nuclei would be little generated. Therefore, uniformnuclei having a narrow range of particle size distribution can be formedby the step for nucleation. On the other hand, in the step for growth ofparticles, nuclei can be homogenously grown up. Therefore, according tothe process for producing the composite hydroxide particles of thepresent invention, uniform nickel composite hydroxide particles having anarrow range of particle size distribution can be obtained.

Hereinafter, the process for nucleation is specifically described.

(A) Metal Compound

As a metal compound, a metal compound having an atomic ratio of a metalcorresponding to the atomic ratio of a metal in the nickel compositehydroxide represented by the general formula (I). The metal compoundcomprises one or at least 2 kinds of metal compounds so that the metalcompound has an atomic ratio of a metal corresponding to the atomicratio of a metal in the nickel composite hydroxide represented by thegeneral formula (I).

It is preferred that the metal compound is usually previously dissolvedin water, in order to uniformly mix the metal compound with an ammoniumion donor. Accordingly, it is preferred that the metal compound haswater solubility. Incidentally, the solution prepared by dissolving themetal compound in water corresponds to the aqueous mixed solution asshown in FIG. 1.

As the metal compound, there can be cited, for example, a salt of aninorganic acid, and the like. As the salt of an inorganic acid, one orat least 2 kinds of salts of an inorganic acid are used so that the saltof an inorganic acid has an atomic ratio of a metal corresponding to theatomic ratio of a metal in the nickel composite hydroxide represented bythe general formula (I). As the salt of an inorganic acid, there can becited, for example, a salt of nitric acid, a salt of sulfuric acid, asalt of chloric acid and the like, and the present invention is notlimited to those exemplified ones. These salts of an inorganic acid canbe used alone or in an admixture of at least 2 kinds. As preferred metalcompounds, for example, nickel sulfate and cobalt sulfate can be cited.

(Additive Element)

In the general formula (I), “M” shows an additive element. The additiveelement is at least one element selected from the group consisting ofMg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W. It is preferred that as acompound containing the additive element, a water soluble compound isused. The compound containing the additive element, there can be cited,for example, magnesium sulfate, aluminum sulfate, sodium aluminate,titanium sulfate, ammonium peroxotitanate, titanium potassium oxalate,vanadium sulfate, ammonium vanadate, chromium sulfate, potassiumchromate, manganese sulfate, zirconium sulfate, zirconium nitrate,niobium oxalate, ammonium molybdate, sodium tungstate, ammoniumtungstate and the like, and the present invention is not limited tothose exemplified ones.

When the additive element is homogenously dispersed in the compositehydroxide particles, to the above-mentioned mixed solution can be addeda compound having the additive element, preferably a compound having awater-soluble additive element. Thereby, the additive element can behomogenously dispersed in the composite hydroxide particles.

In addition, when the surface of the composite hydroxide particles iscovered with the additive element, the surface can be covered with theadditive element by, for example, preparing a slurry of the compositehydroxide particles with an aqueous solution containing a compoundhaving the additive element, and precipitating the additive element onthe surface of the composite hydroxide particles with a crystallizationreaction. In this case, an alkoxide solution of a compound having theadditive element may be used in place of the aqueous solution of acompound having the additive element. Furthermore, the surface of thecomposite hydroxide particles can be covered with the additive elementby spraying an aqueous solution or slurry containing a compound havingthe additive element to the composite hydroxide particles followed bydrying.

Incidentally, when the surface of the composite hydroxide particles iscovered with the additive element, the ratio of the number of metalatoms in the compound having the additive element existing in theaqueous solution for nucleation can be agreed with the ratio of thenumber of metal atoms of the composite hydroxide particles by reducingthe amount of the additive element in an amount which is necessary forcovering the surface.

In addition, the step for covering the surface of the compositehydroxide particles with the additive element may be applied to theparticles after heating the composite hydroxide particles, that is, tothe heat treated particles as described above.

(B) Ammonium Ion Donor

In the ammonium ion donor, ammonium ion plays a role as a complexingagent. As the ammonium ion donor, there can be cited, for example,aqueous ammonia, ammonium sulfate, ammonium chloride, ammoniumcarbonate, ammonium fluoride and the like, and the present invention isnot limited to those exemplified ones.

As the ammonium ion donor, aqueous ammonia is usually used. It ispreferred that the concentration of ammonium ion in the solution fornucleation is 3 to 25 g/L. When the concentration of ammonium ion isless than 3 g/L, since the solubility of a metal ion cannot bemaintained constant, platelike hydroxide primary particles havingregulated shapes and particle diameters cannot be formed, and gelatinousnuclei are likely to be produced, so that the particle size distributionis apt to be broad. On the other hand, when the concentration ofammonium ion exceeds 25 g/L, since the solubility of the metal ionbecomes too higher, and the amount of the metal ion existing in thesolution for nucleation increases, fluctuation of the composition of theresulting nuclei will be generated. The concentration of ammonium ioncan be determined by using an ion meter which has conventionally beenused.

In addition, when the concentration of ammonium varies, the solubilityof a metal ion varies, and therefore, hydroxide particles havinghomogeneous composition is not formed. Therefore, it is preferred thatthe concentration of ammonium is kept constant. Accordingly, it ispreferred that the concentration of ammonium is controlled so that thedifference of the lower limit and the upper limit exists within 5 g/L orso.

(C) Preparation of Aqueous Solution for Nucleation

An aqueous solution for nucleation can be prepared by mixing the metalcompound with the ammonium ion donor. The mixing of the metal compoundwith the ammonium ion donor can be usually carried out by mixing theaqueous solution of the metal compound (the aqueous mixed solution asshown in FIG. 1) with the aqueous solution of the ammonium ion donor(the aqueous solution before reaction as shown in FIG. 1). Incidentally,the aqueous solution before reaction is mixed with an aqueous alkalisolution as a pH control agent as described below.

(D) Concentration of a Metal Compound in the Aqueous Solution forNucleation

It is preferred that the concentration of the metal compound in theaqueous solution for nucleation is from 1 to 2.2 mol/L. When theconcentration of the metal compound in the aqueous solution fornucleation is less than 1 mol/L, although a crystallization reaction ofthe composite hydroxide particles can be carried out, the productivityis lowered since the amount of crystallized product decreases. On theother hand, when the concentration of the metal compound in the aqueoussolution for nucleation exceeds 2.2 mol/L, there is a possibility suchthat crystals are precipitated, and thereby clogging is generated in apipe of equipment. In addition, when at least two kinds of the metalcompound are used, each aqueous solution of a metal compound may beprepared and mixed with each other in a desired ratio so that theconcentration of the metal compound in the aqueous solution fornucleation is included within a predetermined range.

In addition, it is preferred that the amount of the nuclei in theaqueous solution for nucleation is about 30 to about 200 g/L. When theconcentration of the nuclei in the aqueous solution for nucleation isless than 30 g/L, aggregation of the primary particles may beinsufficient. When the concentration of the nuclei in the aqueoussolution for nucleation exceeds 200 g/L, the particle growth may bebiased.

(E) pH of the Aqueous Solution for Nucleation

The pH of the aqueous solution for nucleation is controlled to 12.0 to13.4 at a liquid temperature of the aqueous solution for nucleation of25° C. The present invention has one of characteristics in that the pHof the aqueous solution for nucleation is controlled to a specifiedrange. Since the pH of the aqueous solution for nucleation is controlledas described above, the growth of nuclei is inhibited, and onlynucleation can be predominately carried out. Therefore, the resultingnuclei become homogeneous and have a narrow particle diameterdistribution range. Incidentally, when the pH is higher than 13.4 at theliquid temperature of 25° C., the resulting nuclei may become too fine,and the aqueous solution for nucleation is gelled. In the other hand,when the pH is less than 12.0 at the liquid temperature of 25° C., thegrowth reaction of the nuclei is generated along with the nucleation,and therefore, the range of particle size distribution of the resultingnuclei becomes broad and inhomogeneous. Accordingly, the pH of theaqueous solution for nucleation is from 12.0 to 13.4, preferably from12.2 to 13.4.

The pH of the aqueous solution for nucleation can be controlled by usinga pH control agent. As the pH control agent, there can be cited, forexample, an aqueous alkali solution such as an aqueous solution of analkali metal hydroxide such as sodium hydroxide or potassium hydroxide,and the pH control agent is not limited to those exemplified ones in thepresent invention. The pH of the aqueous solution for nucleation can bedetermined by using a pH meter which has been conventionally used. ThepH control agent may be included in the ammonium ion donor.

The pH control agent may be added to the mixed aqueous solution, and itis preferred that the pH control agent is directly added to the aqueoussolution for nucleation since the pH of the aqueous solution fornucleation is easily controlled. When the pH control agent is directlyadded to the aqueous solution for nucleation, the pH control agent maybe added so that the pH of the aqueous solution for nucleation ismaintained within a specified range by using a pump which enables theflow rate to be controlled while stirring the aqueous solution fornucleation.

Incidentally, in the progress of the nucleation, the pH of the aqueoussolution for nucleation and the concentration and pH of the ammonium ionare changed. Therefore, it is desired that the pH of the aqueoussolution for nucleation and the concentration and pH of the ammonium ionare controlled so that these are maintained within a specified range,respectively, by properly adding the aqueous solution of the ammoniumion donor and the pH control agent. For example, as shown in FIG. 1, thepH of the aqueous solution for nucleation and the concentration of theammonium ion can be controlled so that these are maintained within aspecified range, respectively, by supplying the aqueous solution fornucleation with the mixed aqueous solution.

(F) Amount of the Resulting Nuclei

The amount of the nuclei generated in the course of the step fornucleation is not particularly limited, and is preferably from 0.1 to 2%by mass of the metal compound, and more preferably from 0.1 to 1.5% bymass of the metal compound from the viewpoint of obtaining compositehydroxide particles having a proper particle diameter distribution.

(G) Temperature of the Aqueous Solution for Nucleation

The temperature of the aqueous solution for nucleation is preferably 20°C. or more, and more preferably 20° C. to 60° C. When the temperature ofthe aqueous solution for nucleation is less than 20° C., there is atendency that nuclei are likely to generate, and that its controlbecomes difficult. When the temperature of the aqueous solution fornucleation exceeds 60° C., there is a necessity to use an excess amountof the ammonium ion donor in order to maintain the ammonium ionconcentration to a specified range since ammonia is apt to volatile.

(H) Atmosphere in the Step for Nucleation

The atmosphere in the step for nucleation is not particularly limited,but excessively oxidizable atmosphere is not preferred from theviewpoint of stable growth of nuclei. Accordingly, it is desired thatthe atmosphere in the step for nucleation has an oxygen concentrationless than that of the air. For example, when the step for nucleation iscarried out in the atmosphere having an oxygen concentration of 10% orless by volume of the space of the reaction vessel, the unnecessaryoxidization of particles can be suppressed, and therefore, particleshaving an even particle size can be obtained. The concentration ofoxygen in the atmosphere can be controlled by using, for example, aninert gas such as nitrogen gas. As a means for controlling theconcentration of oxygen in the atmosphere to a predetermined range,there can be cited, for example, there can be cited a method forconstantly flowing an inert gas in the atmosphere.

(I) Manufacturing Facilities

In the step for nucleation, an apparatus, which does not collect aproduct until the reaction is completed, is used. As the apparatus,there can be cited, for example, a batch reaction vessel with which astirrer is equipped, and the like. When such an apparatus is used,particles having a narrow particle size distribution and an evenparticle diameter can be easily obtained, since a problem such thatgrowing particles are collected together with an overflowed liquid canbe avoided as in the case where a general continuous crystallizationapparatus for collecting a product by overflowing is used. In addition,when the reaction atmosphere is controlled, it is desired to use anapparatus which enables the control of the atmosphere, such as anenclosed apparatus. When such an apparatus is used, particles beingexcellent in particle diameter distribution (that is particles having anarrow range of particle size distribution) can be obtained, since thegeneration of nuclei almost evenly progresses.

Next, a particle growth step is specifically described below.

(A) pH of the Aqueous Solution for Particle Growth

The pH of the aqueous solution for particle growth is controlled so asto be 10.5 to 12.0 at a liquid temperature of 25° C. Therefore, nucleiare newly generated little in the aqueous solution for particle growth.

When the pH of the aqueous solution for particle growth is higher than12.0, newly generated nuclei increase, and therefore, hydroxideparticles having a favorable particle diameter distribution cannot beobtained. On the other hand, when the pH of the aqueous solution forparticle growth is less than 10.5, a solubility increases due to theammonium ion donor, and the amount of a metal ion remaining in a liquidunfavorably increases without extraction. Accordingly, the pH of theaqueous solution for particle growth at a liquid temperature of 25° C.is from 10.5 to 12.0, and preferably from 10.5 to 11.8.

Incidentally, it is a boundary condition between the nucleation and thegrowth of nuclear that the pH of the aqueous solution for growth ofparticles is 12 at a liquid temperature of 25° C. Therefore, anycondition of the step for nucleation and the step for growth ofparticles can be selected on the basis whether or not the nuclei areexisted in the aqueous solution for growth of nuclei.

When a large amount of nuclei are generated by controlling the pH in thestep for nucleation to greater than 12 at a liquid temperature of 25°C., and thereafter controlling the pH in the step for growth of nucleito 12 at a liquid temperature of 25° C., a large amount of nuclei existsin the aqueous solution for growth of particles. Therefore, the growthof nuclei occurs preferentially, and the above-mentioned hydroxideparticles having a narrow particle diameter distribution and acomparatively large particle diameter is obtained. On the other hand,when the nuclei are in the condition where the nuclei are not existed inthe aqueous solution for growth of particles, that is, the pH in thestep for nucleation is controlled to 12 at a liquid temperature of 25°C., nuclei which grow up are not existed. Therefore, the nucleationpreferentially occurs. Accordingly, the resulting nuclei grow up, andthe above-mentioned favorable hydroxide particles are obtained bycontrolling the pH in the step for growth of particles to lower than 12at a liquid temperature of 25° C.

In either case, the pH at a liquid temperature of 25° C. in the step forgrowth of particles may be controlled to a value lower than the pH at aliquid temperature of 25° C. in the step for nucleation. The differenceof the pH of the aqueous solution for nucleation and the pH of theaqueous solution for growth of particles is preferably 0.5 or more, andmore preferably 0.7 or more from the viewpoint of obtaining hydroxideparticles having a narrow particle diameter distribution and arelatively large particle diameter.

(B) Preparation of Aqueous Solution for Growth of Particles

In the step for growth of particles, since composite hydroxide particlesare crystallized, metal components and the like contained in the aqueoussolution for growth of particles decrease. Therefore, the aqueoussolution for growth of particles is provided with the mixed aqueoussolution. When the ratio of water which is used as a solvent increasesper the metal compound contained in the aqueous solution for growth ofparticles, the concentration of the mixed aqueous solution supplied tothe aqueous solution for growth of particles is apparently decreases.Therefore, there is a possibility that composite hydroxide particles arenot sufficiently grown up in the step for growth of particles.

Therefore, it is preferred that a part of the aqueous solution fornucleation or a part of the aqueous solution for growth of particles isdischarged from the reaction vessel after the completion of the step fornucleation or in the course of the step for growth of particles. Morespecifically, the supply of the mixed aqueous solution and the like tothe aqueous reaction solution for growth of particles and stirring areterminated, to settle down the nuclei or the composite hydroxideparticles, and the supernatant of the aqueous solution for growth ofparticles is discharged. As a result, since the relative concentrationof the mixed aqueous solution in the aqueous solution for growth ofparticles can be increased, the particle size distribution of thecomposite hydroxide particles can be more narrowed, and the density ofthe composite hydroxide particles can be increased. In addition, whenthe pH of the aqueous solution for nucleation is controlled to form theaqueous solution for growth of particles after the completion of thestep for nucleation, the step for nucleation can be quickly shifted tothe step for growth of particles.

As shown in FIG. 2, the step for growth of particles can be carried outby preparing a quality governing aqueous solution in which the pH andthe concentration of ammonium ion are controlled to a value which issuitable for the step for growth of particles apart from the aqueoussolution for nucleation, adding an aqueous solution containing nucleiwhich is prepared by the step for nucleation in the other reactionvessel to this quality governing aqueous solution, to give an aqueoussolution for growth of particles, and using the resulting aqueoussolution for growth of particles. According to this process, since thestep for nucleation is separated from the step for growth of particles,the conditions of the aqueous solution for nucleation and the aqueoussolution for growth of particles can be controlled so that the conditionis suited for each step. In addition, in the step for growth ofparticles, since the pH of the aqueous solution for growth of particlescan be controlled so as to suite for the growth of particles from thebeginning of the step for growth of particles, the range of the particlesize distribution of nickel composite particles which are formed in thestep for nucleation can be narrowed, and homogeneous particles can beformed.

Also, when the aqueous solution for growth of particles is prepared bycontrolling the pH of the aqueous solution for nucleation, since thestep for growth of particles can be continuously carried out from thestep for nucleation, the step for nucleation can be shifted to the stepfor growth of particles only by controlling the pH of the aqueoussolution for nucleation. In other words, the step for nucleation can beeasily shifted to the step for growth of particles by temporarilyterminating the use of the pH control agent which is used in the aqueoussolution for nucleation.

Incidentally, the pH of the aqueous solution for nucleation and theaqueous solution for growth of particles can be controlled by using a pHcontrol agent. The pH control agent includes, for example, inorganicacids such as sulfuric acid, chloric acid and nitric acid, and the like.Among the inorganic acids, it is preferred that the inorganic acid whichis the same as the acid which constitutes the starting material, metalcompound, for example, sulfuric acid in case of a salt of sulfuric acid.

(C) Controlling of Particle Diameter of Composite Hydroxide Particles

The particle diameter of the composite hydroxide particles can becontrolled by controlling the time period for carrying out the step forgrowth of particles. Accordingly, composite hydroxide particles having adesired particle diameter can be obtained by carrying out the step forgrowth of particles until the particles grow up to a desired particlediameter. Incidentally, the particle diameter of the composite hydroxideparticles can be controlled not only by the step for growth ofparticles, but also by controlling the pH and the amount of the metalcompound used in the step for nucleation. For example, when the amountof the metal compound is increased, and the number of the resultingnuclei is increased by increasing the pH in the course of nucleation orby prolonging the time period of the nucleation, the particle diameterof the resulting composite hydroxide particles can be reduced. On theother hand, when the step for nucleation is carried out so that theamount of the resulting nuclei is decreased, the particle diameter ofthe resulting composite hydroxide particles can be increased.

(D) Other Conditions

The difference between the step for nucleation and the step for growthof particles resides in that the pH regulated in the step for nucleationis different from the pH regulated in the step for growth of particles.Conditions such as the metal compound, concentration of ammonium ion,reaction temperature and atmosphere are substantially the same in thesesteps.

EXAMPLES

Hereinafter, working examples of the present invention will be morespecifically described. However, the present invention is not limited tothose working examples.

The average particle diameter and the particle size distribution of acomposite hydroxide and a cathode active material, which are obtained ineach example and each comparative example, and the performance (initialdischarge capacity, cycle capacity retention rate and resistance ofpositive electrode) of a secondary battery were determined by thefollowing methods:

(Measurement of Average Particle Diameter and Particle SizeDistribution)

The average particle diameter and the particle size distribution (avalue of: [(d90−d10)/average particle diameter]) of a compositehydroxide and a cathode active material are calculated from thevolume-integrated value determined by using a laser diffractionscattering type particle size distribution measurement apparatus(manufactured by Nikkiso Co., Ltd. under the trade name of MicrotrackHRA).

In addition, a crystal structure of a composite hydroxide and a cathodeactive material were determined by means of an X-ray diffractionmeasurement apparatus (PANalytical Ltd. under the trade name of X 'PertPRO), and the compositions of the obtained composite hydroxide andcathode active material were determined by an ICP atomic emissionspectrometry method after dissolving a sample in an amount of 1 g in 100mL of purified water.

(Production of Secondary Battery)

A 2032-type coin battery as shown in FIG. 8 (hereinafter, referred to ascoin-type battery 1) was used for evaluating the performance of asecondary battery.

As shown in FIG. 8, the coin-type battery 1 is composed of a case 2, andan electrode 3 accommodated in this case 2.

The case 2 has a hollow and one-end opened positive electrode can 2 aand a negative electrode can 2 b placed at the opening of this positiveelectrode can 2 a, and constructed so that a space for accommodating theelectrode 3 between the negative electrode can 2 b and the positiveelectrode can 2 a when the negative electrode can 2 b is positioned atthe opening of the positive electrode can 2 a.

The electrode 3 is composed of a positive electrode 3 a, a separator 3 cand negative electrode 3 b, and those are laminated so as to align inthis order. The positive electrode 3 a is contacted with the inner faceof the positive electrode can 2 a, and the negative electrode 3 b isaccommodated in the case 2 so that the negative electrode 3 b iscontacted with the inner face of the negative electrode can 2 b.

Incidentally, the case 2 is provided with a gasket 2 c, and the relativemovements of the positive electrode can 2 a and the negative electrodecan 2 b is inhibited by this gasket 2 c with the keeping of the state ofcontactless of the positive electrode can 2 a and the negative electrodecan 2 b. In addition, the gasket 2 c also has a function to seal the gapbetween the positive electrode can 2 a and the negative electrode can 2b so as to shut the gap between the inside of the case 2 and theexterior in the air-tight and liquid-tight state.

The coin-type battery 1 as described above was produced by the followingmethod.

First of all, 52.5 mg of a cathode active material for a nonaqueouselectrolyte secondary battery, 15 mg of acetylene black and 7.5 mg of apolytetrafluoroethylene resin (PTFE) were mixed together, and theresulting mixture was subjected to press molding at a pressure of 100MPa so as to have a diameter of 11 mm and a thickness of 100 μm, toproduce a positive electrode 3 a. The produced positive electrode 3 awas dried in a vacuum drier at 120° C. for 12 hours.

A coin-type battery 1 as described above was produced by using thispositive electrode 3 a, a negative electrode 3 b, a separator 3 c and anelectrolytic solution in a glove box having an argon atmosphere in whicha dew point was controlled to −80° C. As the negative electrode 3 b,there was used an electrode sheet which was produced by punching acopper foil to a discoid shape having a diameter of 14 mm, and coatedwith graphite powders having an average particle diameter of about 20 μmand polyvinylidene fluoride. Also, as the separator 3 b, a polyethyleneporous membrane having a film thickness of 25 μm was used. As theelectrolytic solution, a mixed solution prepared by mixing ethylenecarbonate (EC) with diethyl carbonate (DEC) in an equal amount, in which1 M LiClO₄ was used as a supporting electrolyte (manufactured byTomiyama Pure Chemical Industries, Limited).

The initial discharge capacity, the cycle capacity retention rate andthe positive electrode resistance for evaluating performance of theproduced coin-type battery 1 were defined as follows:

The initial discharge capacity was determined by allowing to stand thecoin-type battery 1 for about 24 hours, and an electric current densityof 0.1 mA/cm² for the positive electrode was charged up to a cut-offvoltage of 4.3 V after an open circuit voltage (OCV) was stabilized.After the application of voltage was stopped for one hour, the capacitywhen electric discharge was carried out to a cut-off voltage of 3.0 Vwas regarded as an initial discharge capacity.

As to the cycle capacity retention rate, a cycle comprising carrying outthe electric charge up to 4.2 V under the condition of a current densityof 2 mA/cm² and carrying out the electric discharge to 3.0 V wasrepeated 500 times. The ratio of the discharge capacity after the repeatof charge and discharge to the initial discharge capacity was calculatedand its ratio was regarded as a capacity retention rate. When thecapacity of charge and discharge was determined, a multichannelvoltage/electric current generator (manufactured by AdvantestCorporation under the trade name of R6741A,) was used.

In addition, when the positive electrode resistance was determined bycharging the coin-type battery 1 at a charging potential of 4.1 V bymeans of frequency response analyzer and Potentio/Galvanostat(manufactured by Solartron under the product number of 1255B) inaccordance with an alternating current impedance method, a Nyquist plotwas obtained as shown in FIG. 9.

The resistance of the positive electrode resistance was determined bycarrying out a fitting calculation with an equivalent circuit based onthis Nyquist plot.

Incidentally, when composite hydroxides, cathode active materials andsecondary batteries were produced in the working examples, special gradechemicals manufactured by Wako Pure Chemical Industries, Ltd. were used.

Example 1 (Step for Producing Composite Hydroxide)

The composite hydroxides were prepared by carrying out the followingmethods in accordance with the method according to the presentinvention.

First of all, a reaction vessel having a volume of 34 L was charged withwater in a half amount of the volume of the reaction vessel. Thereafter,while stirring the water, the temperature in the reaction vessel wascontrolled to 40° C., and nitrogen gas was introduced into the reactionvessel to form a nitrogen atmosphere in the reaction vessel. At thattime, the concentration of oxygen in the space of the reaction vesselwas 2.0% by volume.

A 25% aqueous sodium hydroxide solution and a 25% aqueous ammonia wereadded into water in the reaction vessel in appropriate amounts, and anaqueous solution before the reaction in the vessel was adjusted to havea pH of 12.6 in terms of the pH as measured at a liquid temperature of25° C. as a standard. Additionally, the ammonia concentration in theaqueous solution before the reaction was adjusted to 15 g/l.

(Step for Nucleation)

Next, nickel sulfate and cobalt sulfate were dissolved in water to givea 1.8 mol/L mixed aqueous solution. In this mixed aqueous solution, themolar ratio of each metal element was controlled so that Ni:Co became0.82:0.15.

The above-mentioned mixed aqueous solution was added to the reactionmixture in the reaction vessel at a rate of 88 ml/min. At the same time,a 25% aqueous ammonia and a 25% aqueous sodium hydroxide solution werealso added to the reaction mixture in the reaction vessel at a constantrate, and nucleation was carried out by carrying out the crystallizationfor 2 minutes and 30 seconds while the concentration of ammonium ion inthe resulting aqueous solution for nucleation was maintained to theabove-mentioned value, and while the pH was controlled to 12.6 (pH fornucleation).

(Step for Particle Growth)

Thereafter, supply of only the 25% aqueous sodium hydroxide solution wasstopped until the pH of the aqueous solution for nucleation became 11.6(pH for growth of particles) at a liquid temperature of 25° C., to givean aqueous solution for growth of particles.

After the pH of the aqueous solution for growth of particles wasattained to 11.6 of a pH as measured at a liquid temperature of 25° C.,supply of the 25% sodium hydroxide aqueous solution was restarted togrow up the particles for 2 hours under the control of the pH to 11.6.

The supply of the aqueous sodium hydroxide solution was terminated, andstirring was also terminated, to allow to stand when the reaction vesselwas filled with the solution in order to accelerate the settling of aproduct. Then, after a half aliquot of the supernatant was drawn outfrom the reaction vessel, the supply of the aqueous sodium hydroxidesolution was restarted, that crystallization was carried out for 2 hours(for 4 hours in total), to terminate the growth of particles.Thereafter, the resulting product was washed with water, filtrated anddried, to collect particles.

The resulting particles were transferred to another reaction vessel andmixed with water at room temperature, to give a mixed aqueous solutionas a slurry. An aqueous solution of sodium aluminate and sulfuric acidwere added to this mixed aqueous solution while stirring so that theslurry was adjusted to have a pH of 9.5. Thereafter, the surface ofnickel-cobalt composite hydroxide particles was covered with aluminumhydroxide by continuing the stirring for 1 hour. At that time, theaqueous solution of sodium aluminate was added to the mixed aqueoussolution so that the molar ratio of the metal elements in the slurry wassatisfied with Ni:Co:Al=0.82:0.15:0.03.

After the stirring was terminated, the aqueous solution was filtered andthe particles which were covered with the aluminum hydroxide were washedwith water, to obtain a composite hydroxide. The resulting compositehydroxide was chemically analyzed. A result, its composition hadNi_(0.82)Co_(0.15)Al_(0.03)(OH)_(2+α) (0≤α≤0.5). When the particle sizedistribution of this composite hydroxide particles were determined, asshown in FIG. 5, the average particle diameter was 4.4 μm, and the valueof [(d90−d10)/average particle diameter] was 0.49.

From an SEM photograph (FIG. 6) which showed the results of observationof the obtained composite hydroxide particles with an SEM (manufacturedby Hitachi High-Technologies Corporation under the trade name ofscanning electron microscope S-4700), it was confirmed that the obtainedcomposite hydroxide particles were nearly spherical, and their particlediameter were almost even.

(Step for Producing Cathode Active Material)

The above-mentioned composite hydroxide particles were thermally treatedin the air flow (concentration of oxygen: 21% by volume) at atemperature of 700° C. for 6 hours, to give composite oxide particles.

Lithium hydroxide was weighed so that the ratio of Li/Me became 1.02,and this lithium hydroxide was mixed with the composite oxide particlesobtained in the above, to give a mixture. The mixing was carried out byusing a shaker-mixer apparatus (manufactured by Willy A Bachofen (WAB)AG under the trade name of TURBULA Type T2C).

Thus resulting mixture was calcined in an oxygen flow (concentration ofoxygen: 100% by volume) at 500° C. for 4 hours, and thereaftercalcinated at 730° C. for 24 hours. Thereafter, the mixture was cooled,and pulverized, to give a cathode active material.

As shown in FIG. 5, the particle size distribution of the obtainedCathode active material was determined. As a result, the averageparticle diameter was 4.5 μm, and the value of [(d90−d10)/averageparticle diameter] was 0.56.

In addition, an SEM observation of the cathode active material wascarried out in the same manner as in the case of the composite hydroxideparticles. As a result, as is clear from the SEM photograph (FIG. 7), itwas confirmed that the obtained cathode active material was nearlyspherical, and had an almost even particle diameter.

In addition, the obtained cathode active material was analyzed asdetermined by a powder X-ray diffraction analysis with a Cu-Kα ray. As aresult, it was confirmed that the positive-electrode active was composedonly of a hexagonal layered crystal of lithium-nickel-cobalt compositeoxide.

Also, the cathode active material was chemically analyzed. As a result,it was confirmed that the cathode active material had a compositioncontaining Li of 7.42% by mass, Ni of 50.4% by mass, Co of 9.24% by massand Al of 0.97% by mass, which showed that the cathode active materialhad a composition of Li_(1.017)Ni_(0.82)CO_(0.15)Al_(0.03)O₂.

(Evaluation of Battery)

A charge and discharge test of a coin-type battery 1 having a positiveelectrode which was formed by using the cathode active material wascarried out. As a result, as shown in FIG. 5, the initial dischargecapacity of the coin-type battery 1 was 190.7 mAh/g, the dischargecapacity after 500 cycles was 154.7 mAh/g, and the capacity retentionrate was 82%. In addition, the resistance of the positive electrode was3.8Ω.

With regard to Examples 2 to 11 and Comparative Examples 1 to 5 asmentioned below, only the substances and conditions which were changedfrom the above-mentioned Example 1 are shown. In addition, the resultsof each evaluation of Examples 2 to 11 and Comparative Examples 1 to 5are shown in FIG. 5.

Example 2

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that lithiumhydroxide was mixed with the composite oxide particles so that Li/Mebecame 1.06 (molar ratio). The performance of the obtained cathodeactive material for a nonaqueous electrolyte secondary battery wasexamined in the same manner as in Example 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.62% bymass, Ni of 49.8% by mass, Co of 9.15% by mass and Al of 0.97% by mass,which showed that the cathode active material had a composition ofLi_(1.056)Ni_(0.82)Co_(0.15)Al_(0.03)O₂, and had a crystal structure ofa hexagonal system as determined by a powder X-ray diffraction.

Example 3

In the step for production of composite hydroxide particles, a mixedaqueous solution was prepared so that the ratio of Ni:Co:Al of the metalelements became 0.83:0.16:0.01 in a molar ratio. A cathode activematerial for a nonaqueous electrolyte secondary battery was obtained inthe same manner as in Example 1 except that the step for nucleation wascarried out so that the pH of the obtained mixed aqueous solution became12.8 at 25° C., and that covering of aluminum hydroxide was not carriedout after the nucleation. The performance of the obtained cathode activematerial for a nonaqueous electrolyte secondary battery was examined inthe same manner as in Example 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.38% bymass, Ni of 50.7% by mass, Co of 9.76% by mass and Al of 0.97% by mass,which showed that the cathode active material had a composition ofLi_(1.021)Ni_(0.83)Co_(0.16)Al_(0.01)O₂, and had a crystal structure ofa hexagonal system as determined by a powder X-ray diffraction.

Example 4

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that theconcentration of ammonium ion was controlled to 10 g/L in the step forproducing composite hydroxide, and that the reaction time period wascontrolled to 30 seconds in the step for nucleation. The performance ofthe obtained cathode active material for a nonaqueous electrolytesecondary battery was examined in the same manner as in Example 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.41% bymass, Ni of 50.2% by mass, Co of 9.23% by mass and Al of 0.96% by mass,which showed that the cathode active material had a composition ofLi_(1.019)Ni_(0.82)CO_(0.15)Al_(0.03)O₂, and had a crystal structure ofa hexagonal system as determined by a powder X-ray diffraction.

Example 5

A composite hydroxide was obtained in the same manner as in Example 1except that the mixed aqueous solution was prepared so that the molarratio of metal elements of Ni:Co:Ti became 0.82:0.15:0.01, thatcrystallization was carried out in the step for producing compositehydroxide, and that covering of aluminum hydroxide was carried out sothat the molar ratio Ni:Co:Ti:Al became 0.82:0.15:0.01:0.02. Theperformance of the obtained cathode active material for a nonaqueouselectrolyte secondary battery was examined in the same manner as inExample 1.

In addition, a cathode active material for a nonaqueous electrolytesecondary battery was obtained in the same manner as in Example 1 exceptthat the temperature for heat treatment was controlled to 550° C. andthat the calcinating temperature was controlled to 745° C. in the stepfor producing a cathode active material by using the obtained compositehydroxide. The performance of the obtained cathode active material for anonaqueous electrolyte secondary battery was examined in the same manneras in Example 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.40% bymass, Ni of 50.2% by mass, Co of 9.21% by mass, Al of 0.6% by mass andTi of 0.5% by mass, which showed that the cathode active material had acomposition of Li_(1.021)Ni_(0.82)Co_(0.15)Al_(0.02)Ti_(0.01)O₂, and hada crystal structure of a hexagonal system as determined by a powderX-ray diffraction.

Example 6

A composite hydroxide was obtained in the same manner as in Example 1except that the mixed aqueous solution was prepared so that the molarratio of the metal elements of Ni:Co:Zr became 0.82:0.15:0.005, thatcrystallization was carried out in the step for producing compositehydroxide, and that covering of aluminum hydroxide was carried out sothat the molar ratio of Ni:Co:Zr:Al became 0.82:0.15:0.005:0.025.

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained and in the same manner as in Example 1 except that thetemperature for heat treatment was controlled to 550° C., and that thecalcinating temperature was controlled to 745° C. in the step forproducing a cathode active material by using the obtained compositehydroxide. The performance of the obtained cathode active material for anonaqueous electrolyte secondary battery was examined in the same manneras in Example 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.35% bymass, Ni of 49.9% by mass, Co of 9.17% by mass, Zr of 0.50% by mole andAl of 0.7% by mass, which showed that the cathode active material had acomposition of Li_(1.021)Ni_(0.82)Co_(0.15)Zr_(0.005)Al_(0.025)O₂, andhad a crystal structure of a hexagonal system as determined by a powderX-ray diffraction.

Example 7

A composite hydroxide was obtained in the same manner as in Example 1except that the mixed aqueous solution was prepared so that the molarratio of the metal elements of Ni:Co:W became 0.82:0.15:0.005, thatcrystallization was carried out in the step for producing compositehydroxide, and that covering of aluminum hydroxide was carried out sothat the molar ratio of Ni:Co:W:Al became 0.82:0.15:0.005:0.025.

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that thetemperature for heat treatment was controlled to 550° C., and that thecalcinating temperature was controlled to 745° C. The performance of theobtained cathode active material for a nonaqueous electrolyte secondarybattery was examined in the same manner as in Example 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.34% bymass, Ni of 49.8% by mass, Co of 9.15% by mass, W of 0.93% by mass andAl of 0.69% by mass, which showed that the cathode active material had acomposition of Li_(1.022)Ni_(0.82)Co_(0.15)W_(0.005)Al_(0.025)O₂, andhad a crystal structure of a hexagonal system as determined by a powderX-ray diffraction.

Example 8

A composite hydroxide was obtained in the same manner as in Example 1except that the metal salt solution was prepared so that the molar ratioof the metal elements of Ni:Co:Ti became 0.82:0.15:0.03, thatcrystallization was carried out in the step for producing compositehydroxide, and that covering of aluminum hydroxide was not carried out.

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that thetemperature for heat treatment was controlled to 400° C., and mixing wascarried out so that Li/Me became 1.06, and that the calcinatingtemperature was controlled to 760° C. in the step for producing acathode active material by using the obtained composite hydroxide. Theperformance of the obtained cathode active material for a nonaqueouselectrolyte secondary battery was examined in the same manner as inExample 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.60% bymass, Ni of 49.7% by mass, Co of 9.16% by mass and Ti of 1.52% by mass,which showed that the cathode active material had a composition ofLi_(1.059)Ni_(0.82)CO_(0.15)Ti_(0.03)O₂, and had a crystal structure ofa hexagonal system as determined by a powder X-ray diffraction.

Example 9

A composite hydroxide was obtained in the same manner as in Example 1except that the mixed aqueous solution was prepared so that the molarratio of the metal elements of Ni:Co:Mn became 0.8:0.1:0.1, thatcrystallization was carried out in the step for producing compositehydroxide, and that covering of aluminum hydroxide was not carried out.

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that thetemperature for heat treatment was controlled to 550° C., that lithiumhydroxide was mixed so that Li/Me became 1.10, and that the calcinatingtemperature was controlled to 800° C. in the step for producing acathode active material by using the obtained composite hydroxide. Theperformance of the obtained cathode active material for a nonaqueouselectrolyte secondary battery was examined in the same manner as inExample 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.84% bymass, Ni of 47.9% by mass, Co of 6.15% by mass and Mn of 5.79% by mass,which showed that the cathode active material had a composition ofLi_(1.101)Ni_(0.80)CO_(0.10)Mn_(0.10)O₂, and had a crystal structure ofa hexagonal system as determined by a powder X-ray diffraction.

Example 10

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that thetemperature in the reaction vessel was controlled to 50° C., that theconcentration of ammonium ion was controlled to 20 g/l, that the pH wascontrolled to 13.2 at a liquid temperature of 25° C., and that thenucleation was carried out for 30 seconds in the step for producingcomposite hydroxide. The performance of the obtained cathode activematerial for a nonaqueous electrolyte secondary battery was examined inthe same manner as in Example 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.43% bymass, Ni of 50.2% by mass, Co of 9.20% by mass and Al of 0.95% by mass,which showed that the cathode active material had a composition ofLi_(1.022)Ni_(0.82)CO_(0.14)Al_(0.03)O₂, and had a crystal structure ofa hexagonal system as determined by a powder X-ray diffraction.

Example 11

A small-size reaction vessel having a volume of 5 L was charged withwater in a half amount of the volume of the reaction vessel, and thetemperature in the reaction vessel was controlled to 40° C. whilestirring. A 25% aqueous sodium hydroxide solution and a 25% aqueousammonia were added thereto in a proper amount so that the pH of thereaction mixture in the reaction vessel became 12.6 at a liquidtemperature of 25° C., and that the concentration of ammonium ion in thereaction mixture became 10 g/L.

Next, a 1.8 mol/L mixed aqueous solution prepared by dissolving nickelsulfate and cobalt sulfate (molar ratio of metal elements ofNi:Co=0.82:0.15), a 25% aqueous ammonia, and a 25% aqueous sodiumhydroxide solution were added to the above-mentioned reaction mixture ata constant rate so that the concentration of ammonium ion in theobtained aqueous solution for nucleation had the above-mentioned value,and the aqueous sodium hydroxide solution was added for 2 minutes and 30seconds while the pH was controlled to 12.6 (pH for nucleation),to giveseed crystals.

Another reaction vessel having a volume of 34 L was charged with waterin a half amount of the volume of the reaction vessel. While stirringthe water, the temperature in the reaction vessel was controlled to 40°C., and nitrogen gas was introduced into the reaction vessel to form anitrogen atmosphere in the reaction vessel. At that time, theconcentration of oxygen in the space of the reaction vessel was 2.0% byvolume.

To the water in this reaction vessel were added a 25% aqueous sodiumhydroxide solution and a 25% aqueous ammonia in a proper amount, tocontrol the pH of the reaction mixture in the reaction vessel to 11.6 ata liquid temperature of 25° C. In addition, the concentration ofammonium ion in the reaction mixture was controlled to 10 g/L. Thereaction mixture containing the seed crystals obtained in theabove-mentioned small-size reaction vessel was added to the reactionvessel, and thereafter, under the condition that the concentration ofammonium ion in the aqueous solution for nucleation was maintained tothe above-mentioned value, the above-mentioned mixed aqueous solution,an aqueous ammonia and a sodium hydroxide aqueous solution werecontinuously added thereto for 2 hours while the pH was controlled to11.6, to carry out the growth of particles.

When the reaction vessel was filled with the liquid, supply of theaqueous ammonia and the aqueous sodium hydroxide solution wasterminated, stirring was terminated, to allow to stand in order toaccelerate the settling of a product. After the product was settleddown, a half aliquot of the supernatant was taken out from the reactionvessel, and then the supply of the aqueous ammonia and the aqueoussodium hydroxide solution was restarted. Furthermore, the aqueousammonia and the aqueous sodium hydroxide solution were supplied to thereaction vessel for additional 2 hours (for 4 hours in total), and thesupply was terminated. The resulting particles were washed with water,filtrated and dried to collect.

The subsequent procedures were carried out in the same manner as inExample 1, to give a cathode active material for a nonaqueouselectrolyte secondary battery. The performance of the obtained cathodeactive material for a nonaqueous electrolyte secondary battery wasexamined in the same manner as in Example 1.

In addition, it was confirmed by a chemical analysis that the obtainedcathode active material had a composition containing Li of 7.34% bymass, Ni of 51.5% by mass and Co of 9.44% by mass, which showed that thecathode active material had a composition ofLi_(1.019)Ni_(0.85)Co_(0.15)O₂, and had a crystal structure of ahexagonal system as determined by a powder X-ray diffraction.

Comparative Example 1

A metal salt solution and an aqueous ammonia solution, which were thesame as used in Example 1, and a liquid neutralizer were continuouslyadded at a constant flow rate to a reaction vessel for continuouscrystallization which was equipped with a pipe for overflowing at a toppart, while maintaining its pH at 25° C. to a constant value of 12.0,and crystallization was carried out by using a usual method includingcontinuously collecting a slurry overflowed. A cathode active materialfor a nonaqueous electrolyte secondary battery was obtained in the samemanner as in Example 1 except that an average retaining period of timein the reaction vessel was controlled to 10 hours, and that thecrystallized product was obtained by collecting a slurry and separatinga solid matter from a liquid matter in the slurry after the equilibriumstate was reached in the continuous vessel. The performance of theobtained cathode active material for a nonaqueous electrolyte secondarybattery was examined in the same manner as in Example 1.

Comparative Example 2

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that the pHduring the nucleation and during the growth was maintained at a constantvalue of 11.6, respectively at a liquid temperature of 25° C. Theperformance of the obtained cathode active material for a nonaqueouselectrolyte secondary battery was examined in the same manner as inExample 1.

Comparative Example 3

A nickel composite hydroxide was obtained in the same manner as inExample 1 except that the pH during the nucleation and during the growthwas maintained at a constant value of 12.6, respectively.

Since new nuclei were generated in the course of the whole period of thecrystallization reaction, particles having an indeterminate form with abroad particle size distribution containing gelatinous deposited matterwere formed. Therefore, the procedures were discontinued due to thedifficulty in solid-liquid separation.

Comparative Example 4

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that thecalcinating was carried out at a temperature of 860° C. for 12 hours andits properties were evaluated. From the results of measurement of X-raydiffraction, it was confirmed that its crystal structure of a hexagonalsystem was deformed, and any performance as a cathode active materialcould not be expected. Therefore, the evaluation of the battery was notcarried out.

Comparative Example 5

A cathode active material for a nonaqueous electrolyte secondary batterywas obtained in the same manner as in Example 1 except that thecalcinating was carried out at 680° C. The performance of the obtainedcathode active material for a nonaqueous electrolyte secondary batterywas examined in the same manner as in Example 1.

(Evaluation)

From the results as shown in FIG. 5, the followings can be understood.

The composite hydroxide particles and cathode active materials obtainedin Examples 1 to 11 were produced in accordance with the presentinvention. Therefore, both of the average particle diameter and thevalue of [(d90−d10)/average particle diameter] which is an index showingthe spread of the particle size distribution are included within adesired range, respectively, and the particles had a favorable particlediameter distribution and an almost even particle diameter. Thecoin-type battery 1 which is produced by using these cathode activematerials had a high initial discharge capacity, is excellent in cyclecharacteristic, and also has a low resistance of a positive electrode.Therefore, the battery has excellent characteristics.

According to Comparative Example 1, since a continuous crystallizationmethod was employed, the nucleation and growth of particles cannot becarried out separately, and since the time period for the growth ofparticles is not constant, its particle size distribution becomesbroader. Therefore, the coin-type battery 1 is poor in cyclecharacteristics although its initial discharge capacity is high.

According to Comparative Example 2, since each pH during the nucleargrowth and during the growth of particles is 12 or less, respectively,the amount of nucleation was insufficient, and thus the compositehydroxide particles and the cathode active material both had largeparticle diameters. Therefore, the coin-type battery 1 in which thiscathode active material was used lacks in reaction surface area, and hasa high resistance of a positive electrode.

According to Comparative Example 3, since each pH during the nucleargrowth and during the growth of particles is 12 or less, respectively,new nuclei are generated in the course of the whole period, andparticles were miniaturized and aggregated. Therefore, the particle sizedistribution becomes broader, and production of a cathode activematerial also becomes difficult.

According to Comparative Examples 4 and 5, since the prosecution forproducing a cathode active materials is different form that in thepresent invention, a cathode active material having favorablecharacteristics could not be obtained. In addition, according toComparative Example 5, it can be seen that the coin-type battery 1 inwhich the cathode active material is used has a high resistance of apositive electrode, and is poor in initial discharge capacity and cyclecharacteristics.

From the foregoing results, it can be seen that the nickel compositehydroxide particles and a nonaqueous electrolyte secondary battery inwhich a cathode active material was used, those of which are obtained ineach working example, have excellent characteristics such as highinitial discharge capacity, excellent cycle characteristics and lowresistance of a positive electrode.

INDUSTRIAL APPLICABILITY

The nonaqueous electrolyte secondary battery of the present invention issuitable for an electric power supply of a small size mobile electronicdevice which constantly requires a high capacity (notebook-sizedpersonal computer, mobile phone terminal, and the like), and is alsosuitable for a battery for an electric automobile which requires a highpower.

In addition, since the nonaqueous electrolyte secondary battery of thepresent invention is excellent in safety, and enables its size reductionand high power, the nonaqueous electrolyte secondary battery is suitablefor an electric power supply for electric automobiles having limitedmounting space.

In addition, the present invention can be adopted not only to anelectric power supply for electric automobiles driven only by electricenergy, but also to an electric power supply for a so-called hybridautomobile in which combustion engine such as a gasoline engine ordiesel engine is used in combination.

DESCRIPTION OF SYMBOLS

-   -   1 coin-type battery    -   2 case    -   3 electrode    -   3 a positive electrode    -   3 b negative electrode    -   3 c separator

1. A process for producing nickel composite hydroxide particles, whereinthe nickel composite hydroxide is represented by the general formula(I):Ni_(1-x-y)Co_(x)M_(y)(OH)_(2+α)  (I) wherein 0≤x≤0.2, 0≤y≤0.15, x+y<0.3,0≤α≤0.5, and M is at least one element selected from the groupconsisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, said processcomprising: a step for nucleation comprising controlling the pH to 12.0to 13.4 at a liquid temperature of 25° C. of an aqueous solution fornucleation containing a metal compound having an atomic ratio of themetals corresponding to the atomic ratio of the metals in the particlesof the nickel composite oxide, and an ammonium ion donor, to carry outnucleation to form an aqueous solution for growth of particlescontaining nuclei, and a step for growth of particles for growing thenuclei, comprising controlling the pH to 10.5 to 12.0 at a liquidtemperature of 25° C. of the aqueous solution for growth of particlesobtained in the step for nucleation to grow the nuclei, wherein the pHin the step for growth of particles is controlled so as to be lower thanthe pH in the step for nucleation.
 2. The process for producing nickelcomposite hydroxide particles, according to claim 1, wherein the aqueoussolution for growth of particles is prepared by controlling the pH ofthe aqueous solution for nucleation after the completion of the step fornucleation.
 3. The process for producing nickel composite hydroxideparticles, according to claim 1, wherein an aqueous solution suitablefor growth of particles is prepared, and the nuclei formed in the stepfor nucleation is added to the aqueous solution, to form the aqueoussolution for nucleation.
 4. The process for producing nickel compositehydroxide particles according to claim 1, wherein a part of the liquidportion of said aqueous solution for growth of particles is discharged,and thereafter the step for growth of particles is carried out.
 5. Theprocess for producing nickel composite hydroxide particles, according toclaim 1, wherein each aqueous solution in the step for nucleation andthe step for growth of particles is maintained to a temperature of 20°C. or more.
 6. The process for producing nickel composite hydroxideparticles, according to claim 1, wherein the concentration of ammoniumion in each aqueous solution in the step for nucleation and the step forgrowth of particles is maintained to be included in the range of 3 to 25g/L.
 7. The process for producing nickel composite hydroxide particles,according to claim 1, wherein the nickel composite hydroxide obtained inthe step for growth of particles is covered with a compound having atleast one of said additive elements in its molecule.
 8. Nickel compositehydroxide particles comprising spherical secondary particles, whereinthe nickel composite hydroxide is represented by the general formula(I):Ni_(1-x-y)Co_(x)M_(y)(OH)_(2+α)  (I) wherein 0≤x≤0.2, 0≤y≤0.15, x+y<0.3,0≤α≤0.5, and M is at least one additive element selected from the groupconsisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, saidspherical secondary particles are formed by the aggregation of pluralplatelike primary particles, and have an average particle diameter of 3to 7 μm; and an index showing the extent of particle size distributionrepresented by the formula: [(d90−d10)/average particle diameter] is0.55 or less.
 9. The nickel composite hydroxide particles, according toclaim 8, wherein said additive element is homogenously distributed inthe secondary particles and/or the surface of the secondary particles ishomogeneously covered with said additive element.
 10. The nickelcomposite hydroxide particles, according to claim 8, wherein said nickelcomposite hydroxide particles are produced by the process wherein thenickel composite hydroxide is represented by the general formula (I):Ni_(1-x-y)Co_(x)M_(y)(OH)_(2+α)  (I) wherein 0≤x≤0.2, 0≤y≤0.15, x+y<0.3,0≤α≤0.5, and M is at least one element selected from the groupconsisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, said processcomprising: a step for nucleation comprising controlling the pH to 12.0to 13.4 at a liquid temperature of 25° C. of an aqueous solution fornucleation containing a metal compound having an atomic ratio of themetals corresponding to the atomic ratio of the metals in the particlesof the nickel composite oxide, and an ammonium ion donor, to carry outnucleation to form an aqueous solution for growth of particlescontaining nuclei, and a step for growth of particles for growing thenuclei, comprising controlling the pH to 10.5 to 12.0 at a liquidtemperature of 25° C. of the aqueous solution for growth of particlesobtained in the step for nucleation to grow the nuclei, wherein the pHin the step for growth of particles is controlled so as to be lower thanthe pH in the step for nucleation.
 11. A process for producing a cathodeactive material for a nonaqueous electrolyte secondary battery, whereinsaid cathode active material comprises a lithium-nickel composite oxiderepresented by the general formula (II):Li_(t)Ni_(1-x-y)Co_(x)M_(y)O₂  (II) wherein 0.95≤t≤1.15, 0≤x≤0.2,0≤y≤0.15, x+y<0.3, and M is at least one element selected from the groupconsisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, said processcomprises: a step for thermally treating the nickel composite hydroxideparticles, according to claim 8, a step for mixing a lithium compoundwith the particles after said thermal treatment, to give a mixture, anda step for calcining said mixture formed in the step for mixing at atemperature of 700° C. to 850° C.
 12. The process for producing thecathode active material for a nonaqueous electrolyte secondary battery,according to claim 11, wherein the number of lithium atoms included inthe mixture to the sum of the numbers of atoms of metals other thanlithium (number of lithium atoms/sum of the numbers of atoms of metalsother than lithium) is controlled to from 0.95/1 to 1.15/1.
 13. Theprocess for producing the cathode active material for a nonaqueouselectrolyte secondary battery, according to claim 11, wherein themixture is preheated at a temperature less than the melting point of thelithium compound and at a temperature capable of the reaction of thelithium compound and the particles after the thermal treatment, prior tothe step for calcining the mixture. 14-16. (canceled)